0001564590-21-008086 | 10-K | XBRL Viewer

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Cover [Abstract]
Entity Registrant Name	FATE THERAPEUTICS, INC.
Entity Central Index Key	0001434316
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Trading Symbol	FATE
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 2,490,000,000
Entity Common Stock, Shares Outstanding		93,783,374
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Tax Identification Number	65-1311552
Entity File Number	001-36076
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	3535 General Atomics Court
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	875-1800
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission, or SEC, on or before the date 120 days after the conclusion of the registrant’s fiscal year ended December 31, 2020 pursuant to Regulation 14A in connection with the registrant’s 2021 Annual Meeting of Stockholders are incorporated by reference into Part III of this annual report on Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 167,347	$ 99,814
Accounts receivable	5,515
Short-term investments and related maturity receivables	315,569	121,613
Prepaid expenses and other current assets	5,892	5,662
Total current assets	494,323	227,089
Long-term investments		39,440
Property and equipment, net	32,308	11,419
Operating lease right-of-use assets	67,084	22,752
Restricted cash	15,227	227
Collaboration contract assets	13,506	1,338
Other assets	9	9
Total assets	622,457	302,274
Current liabilities:
Accounts payable	6,283	5,822
Accrued expenses	15,564	14,697
CIRM award liability, current portion	3,200	2,808
Deferred revenue, current portion	21,144	2,787
Operating lease liabilities, current portion	3,355	1,692
Stock price appreciation milestones, current portion	36,018
Total current liabilities	85,564	27,806
Deferred revenue, net of current portion	46,021	3,775
CIRM award liability, net of current portion	800	702
Operating lease liabilities, net of current portion	93,943	25,235
Stock price appreciation milestones, net of current portion	11,684
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; authorized shares—5,000,000 at December 31, 2020 and December 31, 2019; Class A Convertible Preferred shares issued and outstanding—2,794,549 at December 31, 2020 and December 31, 2019	3	3
Common stock, $0.001 par value; authorized shares—150,000,000 at December 31, 2020 and December 31, 2019; issued and outstanding—87,722,237 at December 31, 2020 and 75,730,260 at December 31, 2019	88	76
Additional paid-in capital	941,216	628,200
Accumulated other comprehensive gain	70	22
Accumulated deficit	(556,932)	(383,545)
Total stockholders’ equity	384,445	244,756
Total liabilities and stockholders’ equity	$ 622,457	$ 302,274

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 31,434	$ 10,680	$ 4,740
Type of Revenue [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 125,623	$ 87,770	$ 56,024
General and administrative	33,896	23,637	15,808
Total operating expenses	159,519	111,407	71,832
Loss from operations	(128,085)	(100,727)	(67,092)
Other income (expense):
Interest income	2,400	4,330	2,190
Interest expense		(1,752)	(1,696)
Change in fair value of stock price appreciation milestones	(47,702)
Total other income (expense), net	(45,302)	2,578	494
Net loss	(173,387)	(98,149)	(66,598)
Other comprehensive loss:
Unrealized gain on available-for-sale securities, net	48	24	1
Comprehensive loss	$ (173,339)	$ (98,125)	$ (66,597)
Net loss per common share, basic and diluted	$ (2.10)	$ (1.44)	$ (1.19)
Weighted-average common shares used to compute basic and diluted net loss per share	82,385,319	68,190,741	56,195,650

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Convertible Preferred Stock
Balance at Dec. 31, 2017	$ 77,189	$ 53	$ 295,934	$ (3)	$ (218,798)	$ 3
Balance (in shares) at Dec. 31, 2017		52,648,601				2,819,549
Exercise of stock options, net of issuance costs	2,693	$ 1	2,692
Exercise of stock options, net of issuance costs (in shares)		694,830
Stock–based compensation	6,293		6,293
Public offering of common stock, net of offering costs	134,791	$ 11	134,780
Public offerings of common stock, net of offering costs (in shares)		10,648,149
Issuance of common stock upon cashless warrant exercise (in shares)		102,101
Issuance of common stock for license agreements	6,100		6,100
Issuance of common stock for license agreements (in shares)		600,000
Unrealized gain on investments	1			1
Net loss	(66,598)				(66,598)
Balance at Dec. 31, 2018	160,469	$ 65	445,799	(2)	(285,396)	$ 3
Balance (in shares) at Dec. 31, 2018		64,693,681				2,819,549
Exercise of stock options, net of issuance costs	2,596	$ 1	2,595
Exercise of stock options, net of issuance costs (in shares)		787,434
Issuance of common stock upon vesting of restricted stock units (in shares)		172,625
Stock–based compensation	17,410		17,410
Public offering of common stock, net of offering costs	162,406	$ 10	162,396
Public offerings of common stock, net of offering costs (in shares)		9,890,000
Issuance of common stock upon cashless warrant exercise (in shares)		61,520
Conversion of preferred shares to common stock (in shares)		125,000				(25,000)
Unrealized gain on investments	24			24
Net loss	(98,149)				(98,149)
Balance at Dec. 31, 2019	244,756	$ 76	628,200	22	(383,545)	$ 3
Balance (in shares) at Dec. 31, 2019		75,730,260				2,794,549
Exercise of stock options, net of issuance costs	9,582	$ 1	9,581
Exercise of stock options, net of issuance costs (in shares)		1,419,117
Issuance of common stock upon vesting of restricted stock units (in shares)		85,000
Stock–based compensation	30,753		30,753
Public offering of common stock, net of offering costs	188,784	$ 7	188,777
Public offerings of common stock, net of offering costs (in shares)		7,108,796
Private placement of common stock, net of issuance costs	49,975	$ 2	49,973
Private placement of common stock, net of issuance costs (in shares)		1,766,160
Issuance of stock to collaboration partner, net of issuance costs	33,934	$ 2	33,932
Issuance of stock to collaboration partner, net of issuance costs (in shares)		1,612,904
Unrealized gain on investments	48			48
Net loss	(173,387)				(173,387)
Balance at Dec. 31, 2020	$ 384,445	$ 88	$ 941,216	$ 70	$ (556,932)	$ 3
Balance (in shares) at Dec. 31, 2020		87,722,237				2,794,549

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net loss	$ (173,387)	$ (98,149)	$ (66,598)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	3,087	2,193	1,204
Stock–based compensation	30,753	17,410	6,293
Amortization of debt discounts and debt issuance costs		115	76
Accretion and amortization of premiums and discounts on investments, net	1,676	(478)	(335)
Amortization of collaboration contract asset	3,110	620	42
Noncash interest expense			373
Deferred rent			192
Deferred revenue	60,603	(8,526)	12,259
Issuance of common stock for license agreement			6,100
Change in fair value of stock price appreciation milestones	47,702
Changes in assets and liabilities:
Accounts receivable	(5,515)	500	(500)
Prepaid expenses and other assets	(13,582)	(1,911)	(2,010)
Accounts payable and accrued expenses	(1,554)	4,277	4,254
Right-of-use assets and lease liabilities, net	7,878	774
Net cash used in operating activities	(39,229)	(83,175)	(38,650)
Investing activities
Purchases of property and equipment	(4,932)	(7,395)	(2,303)
Purchases of investments	(277,344)	(248,858)	(55,660)
Maturities of investments	121,200	98,800	57,500
Net cash used in investing activities	(161,076)	(157,453)	(463)
Financing activities
Issuance of common stock from equity incentive plans, net of issuance costs	9,655	2,522	2,693
Proceeds from public offering of common stock, net of issuance costs	188,784	162,406	134,577
Proceeds from private placement of common stock, net of issuance costs	49,975
Proceeds from sale of common stock to collaboration partner, net of issuance costs	33,934
Proceeds from CIRM award	490		3,510
Principal repayments of long–term debt		(15,000)
Net cash provided by financing activities	282,838	149,928	140,780
Net change in cash, cash equivalents and restricted cash	82,533	(90,700)	101,667
Cash, cash equivalents and restricted cash at beginning of the period	100,041	190,741	89,074
Cash, cash equivalents and restricted cash at end of the period	182,574	100,041	190,741
Supplemental disclosure of cash flow information
Interest paid		2,291	1,242
Supplemental schedule of noncash investing and financing activities
Purchases of property and equipment in accounts payable	1,486	602	$ 37
Right-of-use assets obtained in exchange for lease obligations	$ 49,287	$ 13

Organization and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Summary of Significant Accounting Policies

1. Organization and Summary of Significant Accounting Policies

Organization

Fate Therapeutics, Inc. (the Company) was incorporated in the state of Delaware on April 27, 2007 and has its principal operations in San Diego, California. The Company is a clinical-stage biopharmaceutical company dedicated to the development of programmed cellular immunotherapies for patients with cancer, including off-the-shelf natural killer (NK) and T-cell product candidates derived from clonal master engineered induced pluripotent stem cell (iPSC) lines.

As of December 31, 2020, the Company has devoted substantially all of its efforts to product development, raising capital and building infrastructure and has not generated any revenues from any sales of its therapeutic products. To date, the Company’s revenues have been derived from collaboration agreements and government grants.

Public Equity Offerings

In June 2020, the Company completed a public offering of common stock in which investors, certain of which are affiliated with a director of the Company, purchased 7.1 million shares of its common stock at a price of $28.31 per share under a shelf registration statement. Gross proceeds from the offering were $201.3 million, and after giving effect to $12.5 million of costs related to the offering, net proceeds were $188.8 million.

In September 2019, the Company completed a public offering of common stock in which investors, certain of which are affiliated with a director of the Company, purchased 9.9 million shares of its common stock at a price of $17.50 per share under a shelf registration statement. Gross proceeds from the offering were $173.1 million, and, after giving effect to $10.7 million of costs related to the offering, net proceeds were $162.4 million.

In September 2018, the Company completed a public offering of common stock in which investors, certain of which are affiliated with a director of the Company, purchased 10.6 million shares of its common stock at a price of $13.50 per share under a shelf registration statement. Gross proceeds from the offering were $143.8 million, and, after giving effect to $8.9 million of costs related to the offering, net proceeds were $134.9 million.

Private Placements of Common Stock

In June 2020, in connection with the June 2020 public offering of common stock, the Company exercised its right to cause an existing shareholder, Johnson & Johnson Innovation-JJDC, Inc (JJDC), to purchase $50.0 million of the Company’s common stock, and JJDC purchased in a private placement 1.8 million shares of the Company’s common stock at a price of $28.31 per share, for aggregate proceeds of $50.0 million. In April 2020, in connection with the Janssen Agreement described in Note 2, JJDC purchased in a private placement 1.6 million shares of the Company’s common stock at a price of $31.00 per share, for aggregate proceeds of $50.0 million. The shares of common stock purchased in the private placements were not subject to any underwriting discounts or commissions.

Use of Estimates

The Company’s consolidated financial statements are prepared in accordance with United States generally accepted accounting principles (U.S. GAAP). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to its stock appreciation milestone obligations, contracts containing leases, accrued expenses and the estimated total costs expected to be incurred under the Company’s collaboration agreements. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.

Risks and Uncertainties

Due to the global outbreak of SARS-CoV-2, the novel strain of coronavirus that causes Coronavirus disease 19 (COVID-19), the Company experienced impacts on certain aspects of its business, including its clinical trial and research and development activities, during the year ended December 31, 2020. For example, certain of the Company’s research and development activities have been delayed or disrupted as a result of measures the Company implemented in response to governmental “stay at home” orders and in the interests of public health and safety, and the Company has experienced delays or disruptions in the initiation and conduct of its clinical trials as a result of prioritization of hospital and other medical resources toward pandemic efforts, policies and procedures implemented at clinical sites with respect to the conduct of clinical trials, and other precautionary measures taken in treating patients or in practicing medicine in response to the COVID-19 pandemic. The scope and duration of these delays and disruptions, and the ultimate impacts of COVID-19 on the Company’s operations, are currently unknown. The Company is continuing to actively monitor the situation and may take further precautionary and preemptive actions as may be required by federal, state or local authorities or that it determines are in the best interests of public health and safety and that of the Company’s patient community, employees, partners, and stockholders. The Company cannot predict the effects that such actions, or the impact of COVID-19 on global business operations and economic conditions, may have on its business, strategy, collaborations, or financial and operating results.

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its subsidiaries, Fate Therapeutics Ltd., incorporated in the United Kingdom, Fate Therapeutics, B.V., incorporated in the Netherlands and Tfinity Therapeutics, Inc., incorporated in the United States. To date, the aggregate operations of these subsidiaries have not been significant and all intercompany transactions and balances have been eliminated in consolidation.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating and reportable segment.

Fair Value of Financial Instruments

The Company’s financial instruments consist primarily of cash and cash equivalents, marketable securities, accounts receivable, stock price appreciation milestones, accounts payable, and accrued liabilities. The carrying amounts of accounts receivable, accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the relatively short-term nature of those instruments. Based on the borrowing rates available to the Company for loans with similar terms, which is considered a Level 2 as described below, the Company believes that the fair value of long-term debt approximates its carrying value during the periods when debt was outstanding.

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three- tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. The Company reviews the fair value hierarchy classification on a quarterly basis.

Cash, Cash Equivalents and Restricted Cash

Cash and cash equivalents include cash in readily available checking and savings accounts, money market accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the consolidated statements of cash flows as of December 31, 2020, 2019 and 2018 (in thousands):

	Years Ended December 31,
	2020		2019		2018
Cash and cash equivalents	$	167,347	$	99,814	$	190,514
Restricted cash		15,227		227		227
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$	182,574	$	100,041	$	190,741

In January 2020, the Company entered into a lease for a facility in San Diego that it intends to use as its new corporate headquarters. In lieu of a security deposit, Silicon Valley Bank issued a $15.0 million letter of credit on the Company’s behalf, which letter of credit is secured by a deposit of equal amount. For the years ended December 31, 2020, 2019 and 2018, the restricted cash balance includes cash-collateralized irrevocable standby letters of credit in the amounts of $15.2 million, $0.2 million, and $0.2 million, respectively, associated with the Company’s facilities leases.

Investments

Investments are accounted for as available-for-sale securities and are carried at fair value on the consolidated balance sheets. Upon initial recognition of the investment and at each reporting period, the Company evaluates whether any unrealized losses on investments are attributable to a credit loss or other factors. Any unrealized losses attributable to credit loss are recorded through an allowance for credit losses, limited to the amount by which the fair value is below amortized cost, with the offsetting amount recorded in other income or expense in the consolidated statement of operations and comprehensive loss. Unrealized losses not attributable to an expected credit loss and unrealized gains on investments are recorded in other comprehensive income (loss) on the consolidated statements of operations and comprehensive loss. Realized gains and losses, if any, on investments classified as available-for-sale securities are included in other income or expense.

The amortized cost of investments classified as available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in interest income. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income.

Concentration of Credit Risk

Financial instruments, which potentially subject the Company to a significant concentration of credit risk, consist primarily of cash and cash equivalents and investments. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits and investments are held.

Property and Equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets (generally two to five years) and generally consist of furniture and fixtures, computers, scientific and office equipment, and in-process costs related to facilities construction. Repairs and maintenance costs are charged to expense as incurred.

Impairment of Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. If the carrying amount is not recoverable, the Company measures the amount of any impairment by comparing the carrying value of the asset to the present value of the expected future cash flows associated with the use of the asset. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long-lived assets and, accordingly, has not recognized any impairment losses since inception.

Leases

The Company determines if a contract contains a lease at the inception of the contract. The Company currently has leases related to its facilities leased for office and laboratory space, which are classified as operating leases. These leases result in operating right-of-use (ROU) assets, current operating lease liabilities, and non-current operating lease liabilities in the Company’s consolidated balance sheets. The Company does not have any financing leases. Leases with a term of 12 months or less are considered short-term and ROU assets and lease obligations are not recognized. Payments associated with short-term leases are expensed on a straight-line basis over the lease term.

Lease liabilities represent an obligation to make lease payments arising from the lease and ROU assets represent the right to use the underlying asset identified in the lease for the lease term. Lease liabilities are measured at the present value of the lease payments not yet paid discounted using the discount rate for the lease established at the lease commencement date. To determine the present value, the implicit rate is used when readily determinable. For those leases where the implicit rate is not provided, the Company determines an incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. ROU assets are measured as the present value of the lease payments and also include any prepaid lease payments made and any other indirect costs incurred, and exclude any lease incentives received. Lease terms may include the impact of options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for operating leases is recognized on a straight-line basis over the lease term. The Company aggregates all lease and non-lease components for each class of underlying assets into a single lease component.

Revenue Recognition

The Company recognizes revenue in a manner that depicts the transfer of control of a product or a service to a customer and reflects the amount of the consideration the Company is entitled to receive in exchange for such product or service. In doing so, the Company follows a five-step approach: (i) identify the contract with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations, and (v) recognize revenue when (or as) the customer obtains control of the product or service. The Company considers the terms of a contract and all relevant facts and circumstances when applying the revenue recognition standard. The Company applies the revenue recognition standard, including the use of any practical expedients, consistently to contracts with similar characteristics and in similar circumstances.

A customer is a party that has entered into a contract with the Company, where the purpose of the contract is to obtain a product or a service that is an output of the Company’s ordinary activities in exchange for consideration. To be considered a contract, (i) the contract must be approved (in writing, orally, or in accordance with other customary business practices), (ii) each party’s rights regarding the product or the service to be transferred can be identified, (iii) the payment terms for the product or the service to be transferred can be identified, (iv) the contract must have commercial substance (that is, the risk, timing or amount of future cash flows is expected to change as a result of the contract), and (v) it is probable that the Company will collect substantially all of the consideration to which it is entitled to receive in exchange for the transfer of the product or the service.

A performance obligation is defined as a promise to transfer a product or a service to a customer. The Company identifies each promise to transfer a product or a service (or a bundle of products or services, or a series of products and services that are substantially the same and have the same pattern of transfer) that is distinct. A product or a service is distinct if both (i) the customer can benefit from the product or the service either on its own or together with other resources that are readily available to the customer and (ii) the Company’s promise to transfer the product or the service to the customer is separately identifiable from other promises in the contract. Each distinct promise to transfer a product or a service is a unit of accounting for revenue recognition. If a promise to transfer a product or a service is not separately identifiable from other promises in the contract, such promises should be combined into a single performance obligation.

The transaction price is the amount of consideration the Company is entitled to receive in exchange for the transfer of control of a product or a service to a customer. To determine the transaction price, the Company considers the existence of any significant financing component, the effects of any variable elements, noncash considerations and consideration payable to the customer. If a significant financing component exists, the transaction price is adjusted for the time value of money. If an element of variability exists, the Company must estimate the consideration it expects to receive and uses that amount as the basis for recognizing revenue as the product or the service is transferred to the customer. There are two methods for determining the amount of variable consideration: (i) the expected value method, which is the sum of probability-weighted amounts in a range of possible consideration amounts, and (ii) the mostly likely amount method, which identifies the single most likely amount in a range of possible consideration amounts.

If a contract has multiple performance obligations, the Company allocates the transaction price to each distinct performance obligation in an amount that reflects the consideration the Company is entitled to receive in exchange for satisfying each distinct performance obligation. For each distinct performance obligation, revenue is recognized when (or as) the Company transfers control of the product or the service applicable to such performance obligation.

In those instances where the Company first receives consideration in advance of satisfying its performance obligation, the Company classifies such consideration as deferred revenue until (or as) the Company satisfies such performance obligation. In those instances where the Company first satisfies its performance obligation prior to its receipt of consideration, the consideration is recorded as accounts receivable.

The Company expenses incremental costs of obtaining and fulfilling a contract as and when incurred if the expected amortization period of the asset that would be recognized is one year or less, or if the amount of the asset is immaterial. Otherwise, such costs are capitalized as contract assets if they are incremental to the contract and amortized to expense proportionate to revenue recognition of the underlying contract.

Stock Price Appreciation Milestones

The Company estimates the fair value of the stock price appreciation milestones associated with the Amended and Restated Exclusive License Agreement with Memorial Sloan Kettering Cancer Center, using a Monte Carlo simulation model, which relies on the Company’s current stock price as well as significant estimates and assumptions to determine the estimated liability associated with the contingent milestone payments. The Company accounts for the fair value of the stock price appreciation milestones in accordance with ASC 815, Derivatives and Hedging, with fair value marked to market at each reporting date. The assumptions used to calculate the fair value of the stock price appreciation milestones are subject to a significant amount of judgment including the probability of achieving a specified clinical milestone, the expected volatility of the Company’s common stock, the risk-free interest rate, and the estimated term, which is based in part on the last valid patent claim date. The Company remeasures the fair value of the stock price appreciation milestones at each balance sheet date, with changes in fair value recorded in earnings as non-operating income or expense on the consolidated statements of operations and comprehensive loss.

Research and Development Costs

All research and development costs are expensed as incurred.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Stock-based compensation expense represents the cost of the grant date fair value of employee stock option and restricted stock unit grants recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis. For stock option grants for which vesting is subject to performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable or the performance condition has been achieved. For stock option grants for which vesting is subject to both performance-based milestones and market conditions, expense is recorded over the derived service period after the point when the achievement of the performance-based milestone is probable or the performance condition has been achieved. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, with the exception of option grants for which vesting is subject to both performance-based milestones and market conditions, which are valued using a lattice-based model. The fair value of restricted stock units is based on the closing price of the Company’s common stock as reported on The Nasdaq Global Market on the date of grant. The Company recognizes forfeitures for all awards as such forfeitures occur.

Convertible Preferred Stock

The Company applies the relevant accounting standards to distinguish liabilities from equity when assessing the classification and measurement of preferred stock. Preferred shares subject to mandatory redemptions are considered liabilities and measured at fair value. Conditionally redeemable preferred shares are considered temporary equity. All other preferred shares are considered as stockholders’ equity.

The Company applies the relevant accounting standards for derivatives and hedging (in addition to distinguishing liabilities from equity) when accounting for hybrid contracts that contain conversion options. Conversion options must be bifurcated from the host instruments and accounted for as free-standing financial instruments according to certain criteria. These criteria include circumstances when (i) the economic characteristics and risks of the embedded derivative instruments are not clearly and closely related to the economic characteristics and risks of the host contract, (ii) the hybrid instrument that embodies both the embedded derivative instrument and the host contract is not re-measured at fair value under otherwise applicable accounting principles with changes in fair value reported in earnings as they occurred, and (iii) a separate instrument with the same terms as the embedded derivative instrument would be considered a derivative instrument. The derivative is subsequently measured at fair value at each reporting date, with the changes in fair value reported in earnings.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.

The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes.

The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more- likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.

Comprehensive Loss

Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non‑owner sources. Other comprehensive loss includes unrealized gains and losses, other than losses attributable to a credit loss which are included in other income and expense, on investments classified as available-for-sale securities, which was the only difference between net loss and comprehensive loss for the applicable periods.

Net Loss Per Common Share

Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Dilutive common stock equivalents comprise convertible preferred stock, warrants for the purchase of common stock, and common stock options and restricted stock units outstanding under the Company’s stock option plans. For all periods presented, there is no difference in the number of common shares used to calculate basic and diluted common shares outstanding due to the Company’s net loss position.

Potentially dilutive securities are not included in the calculation of diluted net loss per common share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):

	As of December 31,
	2020		2019		2018
Warrants for common stock		—		—		85,094
Common stock options		10,432,822		9,327,742		6,980,581
Restricted stock units		1,401,732		520,000		188,625
Series A convertible preferred stock (if converted)		13,972,745		13,972,745		14,097,745
Total		25,807,299		23,820,487		21,352,045

Going Concern Assessment

Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year from the financial statement issuance date. The Company determined that there are no conditions or events that raise substantial doubt about its ability to continue as a going concern for a period of at least twelve months from the date of issuance of these financial statements.

Recently Adopted Accounting Pronouncements

In December 2019, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2019-12, Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Accounting Standards Codification (ASC) Topic 740 and amends existing guidance to improve consistent application. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020 and early adoption is permitted. The only exception addressed in ASU 2019-12 applicable to the Company is the elimination of the intra-period exception to allocating income taxes when there are losses from continuing operations. The guidance is to be applied prospectively at the beginning in the year of adoption. The Company elected to early adopt the standard as of January 1, 2020 using the prospective method, and such adoption did not have a material impact on the Company’s consolidated financial statements.

In November 2018, the FASB issued ASU 2018-18, which clarifies the interaction between ASC Topic 808, Collaborative Arrangements, and ASC Topic 606, Revenue from Contracts with Customers. The guidance, among other items, clarifies that certain transactions between collaborative participants should be accounted for as revenue under Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. ASU 2018-18 is effective for fiscal years beginning after December 15, 2019. The Company adopted the standard effective January 1, 2020, and such adoption did not have a material impact on the Company’s consolidated financial statements.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, which amends the disclosure requirements in ASC 820 by adding, changing, or removing certain disclosures. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019. The Company adopted the standard effective January 1, 2020, and such adoption did not have a material impact on the Company’s consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments, which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The standard is effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company adopted the standard effective January 1, 2020 using the modified retrospective approach. Due to the nature of the Company’s investment portfolio, the adoption of the guidance did not have a material effect on the Company’s consolidated financial statements and no allowance was recorded for expected credit losses.

Recently Issues Accounting Pronouncements

In August 2020, the FASB issued ASU 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity's Own Equity (Subtopic 815-40): Accounting 74 for Convertible Instruments and Contracts in an Entity's Own Equity, which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments, and amends existing earnings-per-share, or EPS, guidance by requiring that an entity use the if-converted method when calculating diluted EPS for convertible instruments. ASU 2020-06 is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years, with early adoption permitted for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. The Company plans to adopt ASU 2020-06 effective January 1, 2022 and is currently evaluating the effect ASU 2020-06 will have on its consolidated financial statements and related disclosures.

Collaboration and License Agreements

12 Months Ended

Dec. 31, 2020

Collaboration And License Agreements Disclosure [Abstract]

Collaboration and License Agreements

2. Collaboration and License Agreements

Janssen Collaboration and Option Agreement

On April 2, 2020 (the Effective Date), the Company entered into a Collaboration and Option Agreement (the Janssen Agreement) with Janssen Biotech, Inc. (Janssen), part of the Janssen Pharmaceutical Companies of Johnson & Johnson. Additionally, on the Effective Date, the Company entered into a Stock Purchase Agreement (the Stock Purchase Agreement) with Johnson & Johnson Innovation – JJDC, Inc. (JJDC).

Upon entering the Janssen Agreement, the Company received an upfront, non-refundable and non-creditable payment of $50.0 million. Under the Janssen Agreement, Janssen and the Company will collaborate to develop iPSC-derived CAR NK and CAR T-cell product candidates for the treatment of cancer. Janssen will contribute proprietary antigen binding domains directed to up to four tumor-associated antigen targets (the Janssen Cancer Targets). The Company will research and construct iPSC-derived CAR NK and CAR T-cell product candidates directed to each of the Janssen Cancer Targets (the Collaboration Candidates) and perform preclinical development of Collaboration Candidates. Upon the Company’s completion of activities sufficient to allow the filing of an Investigational New Drug (IND) application for a Collaboration Candidate, Janssen will have the right to exercise an exclusive option and obtain an exclusive license to the Company’s intellectual property rights for the development and commercialization of such Collaboration Candidate. Upon the exercise of such exclusive option, Janssen will be solely responsible for the worldwide clinical development and commercialization of such Collaboration Candidate, and the Company will be primarily responsible for the manufacture, at Janssen’s cost, of such Collaboration Candidate. For each Collaboration Candidate, upon attaining clinical proof-of-concept, the Company shall have the right to elect to co-commercialize and share equally in the profits and losses in the United States, subject to the Company sharing in certain development costs.

Under the terms of the Janssen Agreement, the Company is entitled to receive full funding for all research, preclinical development and IND-enabling activities performed by the Company for Collaboration Candidates, and is eligible to receive (i) with respect to the first Janssen Cancer Target, payments of up to $898.0 million upon the achievement of specified development, regulatory and sales milestones (the Janssen Milestone Payments) for the first Collaboration Candidate, and up to $460.0 million in Janssen Milestone Payments for each additional Collaboration Candidate, directed to the first Janssen Cancer Target; and (ii) with respect to each of the second, third and fourth Janssen Cancer Targets, up to $706.0 million in Janssen Milestone Payments for each of the first Collaboration Candidates, and up to $340.0 million in Janssen Milestone Payments for each additional Collaboration Candidate, directed to the applicable Janssen Cancer Target, where certain Janssen Milestone Payments under (i) and (ii) are subject to reduction in the event the Company elects to co-commercialize and share equally in the profits and losses in the United States of a respective Collaboration Candidate. The Company is further eligible to receive double-digit tiered royalties ranging up to the mid-teens on net sales of Collaboration Candidates that are commercialized by Janssen under the Janssen Agreement, subject to reduction under certain circumstances.

Under the Stock Purchase Agreement, the Company sold 1.6 million shares of common stock to JJDC at $31.00 per share, for an aggregate purchase price of approximately $50.0 million, on April 7, 2020. The Company determined that this common stock purchase represented a premium of $9.93 per share, or $16.0 million in aggregate (the Equity Premium), and the remaining $34.0 million was recorded as an issuance of common stock in shareholders’ equity.

In addition, under the Stock Purchase Agreement, the Company had the right to require JJDC purchase an aggregate of $50.0 million in shares of the Company’s common stock in a private placement at the same price per share as that paid by investors in a public offering. In June 2020, in connection with the Company’s June 2020 public offering, the Company exercised this right and JJDC purchased in a private placement 1.8 million shares of the Company’s common stock at a price of $28.31 per share, for aggregate proceeds of $50.0 million.

Janssen may terminate the Janssen Agreement with respect to one or more Janssen Cancer Targets, or in its entirety, at any time on or after the second anniversary of the Effective Date, and the Company may terminate the Janssen Agreement with respect to a particular Janssen Cancer Target if a Collaboration Candidate has not been selected for IND-enabling studies for such Janssen Cancer Target within specified time periods under certain conditions. The Janssen Agreement contains customary provisions for termination by either party in the event of a material breach of the Janssen Agreement, subject to cure, by the other party and in the event of any bankruptcy, insolvency or similar events with respect to the other party.

The Company applied ASC 808, Collaborative Arrangements (ASC 808) and determined the Janssen Agreement is applicable to such guidance. The Company concluded that Janssen represented a customer and applied relevant guidance from ASC 606, Revenue from Contracts with Customers (ASC 606) to evaluate the appropriate accounting for the Janssen Agreement. In accordance with this guidance, the Company identified its potential performance obligations, including its grant of a license to Janssen to certain of its intellectual property subject to certain conditions, its conduct of research and development services, and its participation in various joint oversight committees. The Company determined that its grant of a license to Janssen to certain of its intellectual property subject to certain conditions was not distinct from other performance obligations because such grant is dependent on the conduct and results of the research and development services. Accordingly, the Company determined that its grant of a license to Janssen and its conduct of research and development services should be accounted for as one combined performance obligation, and that the combined performance obligation is transferred over the expected term of the conduct of the research and development services, which is estimated to be four years. Additionally, the Company determined that participation in the various joint oversight committees did not constitute a performance obligation as the Company’s participation in the various joint oversight committees does not transfer a service.

The Company also assessed the effects of any variable elements under the Janssen Agreement. Such assessment evaluated, among other things, the funding to be received by the Company for its conduct of research and development services. Based on its assessment, the Company concluded that the total amount to be received by the Company for its conduct of research and development services is variable and cannot be readily estimated and, therefore, no amounts associated with such services were included in the initial transaction price. In addition, the Company also assessed its likelihood of receiving (i) preclinical milestones, (ii) various clinical, regulatory and commercial milestone payments, and (iii) royalties on net sales of the Collaboration Candidates. Based on the likelihood of receiving such milestone payments and royalties, no amounts associated with milestones or royalties were included in the initial transaction price.

In accordance with ASC 606, the Company determined that the initial transaction price under the Janssen Agreement equals $66.0 million, consisting of the upfront, non-refundable and non-creditable payment of $50.0 million and the Equity Premium of $16.0 million. The Company concluded that there was not a significant financing component under the Janssen Agreement. The upfront payment of $66.0 million was recorded as deferred revenue and is being recognized as revenue consistent with the Company’s efforts related to the conduct of research and development services, as the research and development services are the primary component of the combined performance obligation. Since the total amount to be received by the Company for its research and development services under the Janssen Agreement could not be readily estimated, revenue associated with the upfront payment will be recognized based on actual headcount utilized as a percentage of total headcount expected to be utilized over the expected term of the conduct of the research and development services. Revenue associated with the research and development services will be recognized in an amount equal to the actual costs incurred during the period in which the research and development services are performed by the Company.

As a direct result of the Company’s entry into the Janssen Agreement, the Company incurred $13.3 million in sublicense fees to certain of its existing licensors. The $13.3 million in sublicense consideration represents an asset under ASC 340, Other Assets and Deferred Costs (ASC 340) and is amortized to research and development expense ratably with the Company’s revenue recognition under the Janssen Agreement. During the year ended December 31, 2020, the Company recognized $1.3 million of such expense. As of December 31, 2020, the Janssen Agreement contract asset balance was $12.0 million.

The Company recognized revenue of $16.8 million under the Janssen Agreement for the year ended December 31, 2020. Such revenue comprised $10.3 million associated with research and development services and $6.5 million associated with the upfront fee and Equity Premium for the year ended December 31, 2020. As of December 31, 2020, aggregate deferred revenue related to the Janssen Agreement was $59.5 million, of which $16.3 million is classified as current.

As of December 31, 2020, the Company has received $4.8 million in cash in aggregate research and development fees from Janssen. As of December 31, 2020, the Company’s entire accounts receivable balance comprised amounts owed from Janssen.

Ono Collaboration and Option Agreement

On September 14, 2018, the Company entered into a Collaboration and Option Agreement (the Ono Agreement) with Ono Pharmaceutical Co. Ltd. (Ono) for the joint development and commercialization of two off-the-shelf iPSC-derived chimeric antigen receptor (CAR) T-cell product candidates. The first off-the-shelf, iPSC-derived CAR T-cell candidate (Candidate 1) targets an antigen expressed on certain lymphoblastic leukemias, and the second off-the-shelf, iPSC-derived CAR T-cell candidate (Candidate 2) targets a novel antigen identified by Ono expressed on certain solid tumors (each a Candidate and collectively the Candidates).

On December 4, 2020, the Company and Ono entered into a letter agreement (the Ono Letter Agreement) in connection with the Ono Agreement. Pursuant to the Ono Letter Agreement, Ono delivered to the Company proprietary antigen binding domains targeting an antigen expressed on certain solid tumors and nominated such antigen binding domains as the Ono Antigen Binding Domain for incorporation into Collaboration Candidate 2. In connection with such nomination and pursuant to the original agreement, in December 2020, Ono paid the Company a milestone fee of $10.0 million for further research and development of Collaboration Candidate 2 and Ono maintains its option to this candidate. In addition, in connection with the Ono Letter Agreement, Fate and Ono agreed to the termination of the Ono Agreement with respect to Collaboration Candidate 1. Fate retains all rights, in its sole discretion, to research, develop and commercialize Collaboration Candidate 1 throughout the world without any obligation to Ono.

Pursuant to the Ono Agreement, the Company and Ono are jointly conducting research and development activities under a joint development plan, with the goal of advancing Candidate 2 to a pre-defined preclinical milestone. The Company has granted to Ono, during a specified period of time, an option to obtain an exclusive license under certain intellectual property rights to develop and commercialize Candidate 2 in all territories of the world, with the Company retaining the right to co-develop and co-commercialize Candidate 2 in the United States and Europe under a joint arrangement whereby it is eligible to share at least 50% of the profits and losses (the Option).

The Option will expire upon the earliest of: (a) the achievement of the pre-defined preclinical milestone, (b) termination by Ono of research and development activities for the Candidate and (c) the date that is the later of (i) four years after the Effective Date and (ii) completion of all applicable activities contemplated under the joint development plan (the Option Period). The Company has maintained worldwide rights of manufacture for Candidate 2.

Under the terms of the Ono Agreement, Ono paid the Company an upfront, non-refundable and non-creditable payment of $10.0 million in connection with entering into the agreement. Additionally, as consideration for the Company’s conduct of research and preclinical development under a joint development plan, Ono pays the Company annual research and development fees set forth in the annual budget included in the joint development plan, which fees are estimated to be $20.0 million in aggregate over the course of the joint development plan.

Further, under the terms of the Ono Agreement, Ono has agreed to pay the Company up to an additional $20.0 million, subject to the exercise by Ono of the Option (Option Exercise Fees) during the Option Period for Candidate 2. Such fees are in addition to the upfront payment research and development fees, and the previously paid $10.0 milestone associated with the Ono Letter Agreement.

Subject to Ono’s exercise of the Option and to the achievement of certain clinical, regulatory and commercial milestones (Milestones) with respect to the Candidate in specified territories, the Company is entitled to receive an aggregate of up to $885.0 million in additional milestone payments for Candidate 2, with the applicable milestone payments for Candidate 2 for the United States and Europe subject to reduction by 50% if the Company elects to co-develop and co-commercialize Candidate 2 as described above. The Company is also eligible to receive tiered royalties (Royalties) ranging from the mid-single digits to the low-double digits based on annual net sales by Ono for Candidate 2 in specified territories, with such royalties subject to certain reductions.

No milestone payments specific to Candidate 1 are payable under the Ono Agreement, given the termination of such candidate under the agreement.

The Ono Agreement will terminate with respect to a Candidate if Ono does not exercise its Option for a Candidate within the Option Period, or in its entirety if Ono does not exercise any of its Options for the Candidates within their respective Option Periods. In addition, either party may terminate the Ono Agreement in the event of breach, insolvency or patent challenges by the other party; provided, that Ono may terminate the Ono Agreement in its sole discretion (x) on a Candidate-by-Candidate basis at any time after the second anniversary of the effective date of the Ono Agreement or (y) on a Candidate-by-Candidate or country-by-country basis at any time after the expiration of the Option Period, subject to certain limitations. The Ono Agreement will expire on a Candidate-by-Candidate and country-by-country basis upon the expiration of the applicable royalty term, or in its entirety upon the expiration of all applicable payment obligations under the Ono Agreement.

The Company applied ASC 808 to the Ono Agreement and Ono Letter Agreement and determined that the agreements are applicable to such guidance. The Company concluded that Ono represented a customer and applied relevant guidance from ASC 606 to evaluate the appropriate accounting for the Ono Agreement and the Ono Letter Agreement. In accordance with this guidance, the Company identified its performance obligations, including its grant of a license to Ono to certain of its intellectual property subject to certain conditions, its conduct of research services, and its participation in a joint steering committee. The Company determined that its grant of a license to Ono to certain of its intellectual property subject to certain conditions was not distinct from other performance obligations because such grant is dependent on the conduct and results of the research services. Additionally, the Company determined that its conduct of research services was not distinct from other performance obligations since such conduct is dependent on the guidance of the joint steering committee. Accordingly, the Company determined that all performance obligations should be accounted for as one combined performance obligation, and that the combined performance obligation is transferred over the expected term of the conduct of the research services, which is estimated to be four years. The termination of Candidate 1 under the Ono Agreement did not impact this assessment.

The Company also assessed, in connection with the upfront, non-refundable and non-creditable payment of $10.0 million received in September 2018 and the $5.0 million prepayment of the first-year research and development fees in October 2018 and concluded that there was not a significant financing component to the Ono Agreement.

The Company also assessed the effects of any variable elements under the Ono Agreement. Such assessment evaluated, among other things, the likelihood of receiving (i) preclinical milestone and option fees, (ii) various clinical, regulatory and commercial milestone payments, and (iii) royalties on net sales of either product Candidate. Based on its assessment, the Company concluded that, based on the likelihood of these variable components occurring, there was not a significant variable element included in the transaction price. Accordingly, the Company has not assigned a transaction price to any Ono Option Milestone, Ono Milestones or Ono Option Exercise Fees, other than the $10.0 million milestone triggered as part of the Ono Letter Agreement in December 2020, given the substantial uncertainty related to their achievement and has not assigned a transaction price to any Ono Royalties.

In accordance with ASC 606, the Company determined that the initial transaction price under the Ono Agreement equals $30.0 million, consisting of the upfront, non-refundable and non-creditable payment of $10.0 million and the aggregate estimated research and development fees of $20.0 million. The upfront payment of $10.0 million was recorded as deferred revenue and is being recognized as revenue over time in conjunction with the Company’s conduct of research services as the research services are the primary component of the combined performance obligations. Revenue associated with the upfront payment will be recognized based on actual costs incurred as a percentage of the estimated total costs expected to be incurred over the expected term of conduct of the research services. The Company recorded the $5.0 million prepayment of the first-year research and development fees as deferred revenue, and such fees were recognized as revenue as the research services were delivered.

In accordance with ASC 606, the Company concluded that the $10.0 million milestone payment associated with the Ono Letter Agreement represented an increase in the initial transaction price under the Ono Agreement in the form of the receipt of variable consideration that was previously constrained. The milestone payment of $10.0 million was recorded to deferred revenue for the proportional percentage of remaining costs to be incurred under the Ono Agreement as a percentage of the estimated total costs expected to be incurred over the expected term of conduct of the research services and is being recognized as revenue over the expected term in conjunction with the Company’s conduct of research services as the research services are the primary component of the combined performance obligations. The Company recognized revenue associated with the milestone payment for the proportional percentage of actual costs incurred under the Ono Agreement as a percentage of the estimated total costs expected to be incurred over the expected term of conduct of the research services.

As a direct result of the Company’s entry into the Ono Agreement and the Ono Letter Agreement, the Company incurred an aggregate of $4.0 million in sublicense consideration to existing licensors of the Company. The $4.0 million in sublicense consideration represents an asset under ASC 340 and is being amortized to research and development expense ratably with the Company’s revenue recognition under the Ono Agreement. During the years ended December 31, 2020 and 2019, the Company recognized $1.8 million and $0.6 million, respectively, of such expense. As of December 31, 2020, the Ono Agreement contract asset had a balance of $1.5 million.

The Company recognized revenue of $14.6 million, $9.3 million, and $0.6 million under the Ono Agreement and Ono Letter Agreement during the years ended December 31, 2020, 2019 and 2018, respectively. Such revenue comprised $6.1 million associated with the Ono Letter Agreement milestone earned in December 2020, $5.7 million associated with research services and $2.8 million associated with the upfront payment during the year ended December 31, 2020. Such revenue comprised $6.2 million associated with research services and $3.1 million associated with the upfront payment during the year ended December 31, 2019, and $0.4 million associated with research services and $0.2 million associated with the upfront payment during the year ended December 31, 2018. As of December 31, 2020, aggregate deferred revenue related to the Ono Agreement and Ono Letter Agreement was $7.7 million, of which $4.8 million is classified as current.

As of December 31, 2020, the Company has received $12.3 million in cash of aggregate research and development fees from Ono.

Juno Collaboration and License Agreement

On May 4, 2015, the Company entered into a strategic research collaboration and license agreement (the Juno Agreement) with Juno Therapeutics, Inc. (Juno) to screen for and identify small molecules that enhance the therapeutic properties of Juno’s genetically-engineered T-cell immunotherapies. The four-year initial research term under the Juno Agreement concluded as scheduled on May 4, 2019, and the overall agreement was terminated upon the receipt of the last quarterly research payment of $0.2 million, which occurred in May 2019.

The Company applied ASC 606 to evaluate the appropriate accounting for the Juno Agreement. In accordance with this guidance, the Company identified its performance obligations, including its grant of an exclusive worldwide license to certain of its intellectual property subject to certain conditions, its conduct of research services and its participation in a joint research committee.

No revenue was recognized under the Juno Agreement during the year ended December 31. 2020. Total revenue recognized under the Juno Agreement during the year ended December 31, 2019 was $1.4 million, which comprised $0.7 million associated with the upfront fee and equity premium, and $0.7 million associated with research services. Total revenue recognized under the Juno Agreement for the year ended December 31, 2018 was $4.1 million, which comprised $2.1 million associated with the upfront fee and the equity premium and $2.0 million associated with research services.

Memorial Sloan Kettering Cancer Center License Agreement

On May 15, 2018, the Company entered into an Amended and Restated Exclusive License Agreement (the Amended MSK License) with Memorial Sloan Kettering Cancer Center (MSK). The Amended MSK License amends and restates the Exclusive License Agreement entered into between the Company and MSK on August 19, 2016 (the Original MSK License), pursuant to which the Company entered into an exclusive license agreement with MSK for rights relating to compositions and methods covering iPSC-derived cellular immunotherapy, including T-cells and NK-cells derived from iPSCs engineered with CARs.

Pursuant to the Amended MSK License, MSK granted to the Company additional licenses to certain patents and patent applications relating to new CAR constructs and off-the-shelf CAR T cells, including the use of clustered regularly interspaced short palindromic repeat (CRISPR) and other innovative technologies for their production, in each case to research, develop, and commercialize licensed products in the field of all human therapeutic uses worldwide. The Company has the right to grant sublicenses to certain licensed rights in accordance with the terms of the Amended MSK License, in which case it is obligated to pay MSK a percentage of certain sublicense income received by the Company.

The Company issued 500,000 shares of the Company’s common stock to MSK (the MSK Shares) and, in return, MSK returned its entire interest in Tfinity Therapeutics, Inc. (Tfinity) to the Company. As a result, as of the effective date of the Amended MSK License, Tfinity is a wholly-owned subsidiary of the Company. The MSK Shares were issued pursuant to an exemption from registration under the Securities Act of 1933, as amended (the Securities Act), in reliance on Section 4(a)(2) of the Securities Act regarding transactions by an issuer not involving a public offering. Additionally, the Company paid an upfront fee of $0.5 million.

During the year ended December 31, 2018, the Company recognized an aggregate of $5.3 million of research and development expenses, consisting of the $0.5 million upfront cash payment to MSK and the issuance of the MSK Shares, valued at $4.8 million, associated with the Amended MSK License.

The Company is obligated to pay to MSK an annual license maintenance fee during the term of the agreement, and milestone payments upon the achievement of specified clinical, regulatory and commercial milestones for licensed products as well as royalty payments on net sales of licensed products

In the event a licensed product achieves a specified clinical milestone, MSK is then eligible to receive certain milestone payments totaling up to $75.0 million based on the price of the Company’s common stock, where the amount of such payments owed to MSK is contingent upon certain increases in the price of the Company’s common stock following the date of achievement of such clinical milestone. These payments are based on common stock price multiples, with the numerator being the fair value of the ten-trading day trailing average closing price of the Company’s common stock and the denominator being the ten-trading day trailing average closing price of the Company’s common stock as of the effective date of the Amended MSK License, adjusted for any stock splits, cash dividends, stock dividends, other distributions, combinations, recapitalizations, or similar events. Under the terms of the Amended MSK License, upon a change of control of the Company, in certain circumstances, the Company may be required to pay a portion of these payments to MSK based on the price of the Company’s common stock in connection with such change of control.

The following table summarizes the common stock multiples and the stock price appreciation milestone payments, none of which have been triggered as of December 31, 2020:

Common stock multiple	5.0x		10.0x		15.0x
Ten-trading day trailing average common stock price	$	50.18	$	100.36	$	150.54
Stock price appreciation milestone payment (in millions)	$	20.0	$	30.0	$	25.0

To determine the estimated fair value of the stock price appreciation milestones, the Company uses a Monte Carlo simulation methodology which models future Company common stock prices based on the current stock price and several key variables. The following variables were incorporated in the calculation of the estimated fair value of the stock price appreciation milestones as of December 31, 2020:

	Year Ended December 31,
	2020
Risk-free interest rate		1.5	%
Expected volatility		78.1	%
Estimated term (in years)		18.0
Closing stock price as of measurement date	$	90.93

The key inputs to the Monte Carlo simulation to determine the fair value of the stock price appreciation milestones include the Company’s stock price as of the measurement date; the estimated term which is based in part on the last valid patent claim date; the expected volatility of the Company’s common stock, estimated using the Company’s historical common stock volatility as of the remeasurement date; and the risk-free rate based on the U.S. Treasury yield for the estimated term determined. Fair value measurements are highly sensitive to changes in these inputs and significant changes could result in a significantly higher or lower fair value and resulting expense or gain.

As the stock price appreciation milestones are first contingent upon the achievement of a specified clinical milestone, the Company estimates the fair value of the stock price appreciation milestones based on the probability of achieving the clinical milestone. This assessment is based on several factors including the successful achievement of technological, manufacturing, and regulatory requirements.

At each balance sheet date, the Company remeasures the fair value of the stock price appreciation milestones, with changes in fair value recognized as a component of other income (expense) in the consolidated statements of operations and comprehensive loss. Amounts are included in current or non-current liabilities based on the estimated timeline associated with the individual potential payments. During the year ended December 31, 2020, the Company recorded $47.7 million of expense associated with the change in fair value of the stock price appreciation milestones. As of December 31, 2020, the Company recorded a liability of $47.7 million associated with the stock price appreciation milestones for the Amended MSK License.

To date, no licensed products have achieved the specified clinical milestone, and no stock price appreciation milestone payments are currently owed to MSK.

Gladstone License Agreement

On September 11, 2018, the Company entered into an exclusive license agreement (the Gladstone License Agreement) with the J. David Gladstone Institutes (Gladstone).

Pursuant to the Gladstone License Agreement, Gladstone granted to the Company exclusive licenses to certain patents and patent applications (the Patent Rights) for the research, development, manufacturing, and commercialization of human therapeutics derived from iPSCs. The Patent Rights cover the use of the CRISPR and engineered nuclease-deactivated CRISPR-associated protein-9 (dCas9) system, known as the CRISPR activation (CRISPRa) system, for cellular reprogramming and iPSC generation.

In consideration for the rights granted under the Gladstone License Agreement, the Company issued to Gladstone 100,000 shares of the Company’s common stock (the Gladstone Shares). The Gladstone Shares were issued pursuant to an exemption from registration under the Securities Act, in reliance on Section 4(a)(2) of the Securities Act regarding transactions by an issuer not involving a public offering.

Additionally, the Company paid Gladstone an upfront fee of $0.1 million and is obligated to pay Gladstone milestone payments in an aggregate amount of up to approximately $1.9 million upon the achievement of specified clinical, regulatory and commercial milestones as well as tiered royalties in the low single digits on net sales of human therapeutic products covered by the Patent Rights. The Company is also obligated to pay Gladstone a tiered percentage in the low- to mid-single digits of certain income received by the Company in connection with the sublicense of the Patent Rights.

During the year ended December 31, 2018, the Company recognized an aggregate of $1.4 million of research and development expenses, consisting of the $0.1 million upfront cash payment to Gladstone and the issuance of the Gladstone Shares, valued at $1.3 million, associated with the Gladstone License Agreement.

Investments

12 Months Ended

Dec. 31, 2020

Investments [Abstract]

Investments

4. Investments

The Company invests portions of excess cash in United States treasuries, commercial paper, non-U.S. government securities, municipal securities, and corporate debt securities with maturities ranging from three to eighteen months from the purchase date. These investments are accounted for as available-for-sale securities and are classified as short-term and long-term investments in the accompanying consolidated balance sheets based on each security’s contractual maturity date.

The following table summarizes the Company’s investments accounted for as available-for-sale securities as of December 31, 2020 and 2019 (in thousands):

	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
December 31, 2020
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	39,736	$	—		$	31	$	39,767
Non-U.S. government securities	1 or less		5,054		—			2	$	5,056
Municipal securities	1 or less		3,082		(1	)		—	$	3,081
Corporate debt securities	1 or less		159,947		(68	)		124	$	160,003
Commercial paper	1 or less		107,680		(18	)		—	$	107,662
Total short-term investments		$	315,499	$	(87	)	$	157	$	315,569

December 31, 2019
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	50,445	$	(4	)	$	16	$	50,457
Corporate debt securities	1 or less		71,171		(24	)		9		71,156
Total short-term investments		$	121,616	$	(28	)	$	25	$	121,613
Classified as non-current assets:
U.S. Treasury debt securities	Greater than 1	$	9,841	$	—		$	5	$	9,846
Corporate debt securities	Greater than 1		29,572		(1	)		23		29,594
Total long-term investments		$	39,413	$	(1	)	$	28	$	39,440

As of December 31, 2020 and 2019, the Company had $1.5 million and $1.0 million, respectively, of accrued interest on investments recorded in prepaid expenses and other assets on the consolidated balance sheets.

The Company reviews its investment holdings at the end of each reporting period and evaluates any unrealized losses using the expected credit loss model to determine if the unrealized loss is a result of a credit loss or other factors. The Company also evaluates its investment holdings for impairment using a variety of factors including the Company’s intent to sell the underlying securities prior to maturity and whether it is more likely than not that the Company would be required to sell the securities before the recovery of their amortized basis. During the years ended December 31, 2020, 2019 and 2018, the Company did not recognize any impairment or realized gains or losses on sales of investments, and the Company did not record an allowance for, or recognize, any expected credit losses.

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

5. Fair Value Measurements

The following tables presents the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2020 and 2019 (in thousands):

			Fair Value Measurements at Reporting Date Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020:
Financial assets:
Money market funds	$	167,347	$	167,347	$	—	$	—
U.S. Treasury debt securities		39,767		39,767		—		—
Non-U.S. government securities		5,056		—		5,056		—
Municipal securities		3,081		—		3,081		—
Corporate debt securities		160,003		—		160,003		—
Commercial paper		107,662		—		107,662		—
Total assets measured at fair value on a recurring basis	$	482,916	$	207,114	$	275,802	$	—

Financial liabilities:
Stock price appreciation milestones	$	47,702	$	—	$	—	$	47,702
Total financial liabilities measured at fair value on a recurring basis	$	47,702	$	—	$	—	$	47,702

As of December 31, 2019:
Financial assets:
Money market funds	$	84,814	$	84,814	$	—	$	—
U.S. Treasury debt securities		60,303		60,303		—		—
Corporate debt securities		100,750		—		100,750		—
Total financial assets measured at fair value on a recurring basis	$	245,867	$	145,117	$	100,750	$	—

Level 1 assets consisted of money market funds and U.S. Treasury securities measured at fair value based on quoted prices in active markets as provided by the Company’s investment managers.

Level 2 assets consisted of corporate debt securities, commercial paper, municipal securities, and non-U.S. government securities measured at fair value using standard observable inputs, including reported trades, broker/dealer quotes, and bids and/or offers. The Company validates the quoted market prices provided by its investment managers by comparing the investment managers’ assessment of the fair values of the Company's investment portfolio balance against the fair values of the Company's investment portfolio balance obtained from an independent source.

There were no Level 3 assets held by the Company as of December 31, 2020.

Level 3 liabilities consisted of stock price appreciation milestones associated with the Amended MSK License as described in detail in Note 2. To determine the estimated fair value of the stock price appreciation milestones, the Company uses a Monte Carlo simulation methodology which models future Company common stock prices based on several key variables. The assumptions used to calculate the fair value of the stock price appreciation milestones are subject to a significant amount of judgment including the expected volatility of the Company’s common stock and estimated term, which is based in part on the last valid patent claim date. Fair value measurements are highly sensitive to changes in these inputs and significant changes could result in a significantly higher or lower fair value and resulting expense or gain. Further, as the stock price appreciation milestones are first contingent upon the achievement of a specified clinical milestone, the Company also estimates the fair value of the stock price appreciation milestones based on the probability of achieving the clinical milestone. This assessment is based on several factors including the successful achievement of technological, manufacturing, and regulatory requirements.

A small change in the assumptions and other inputs, such as the price of the Company’s common stock, may have a relatively large change in the estimated fair value of the stock price appreciation milestones and associated liability and expense. For example, keeping all other variables constant, a hypothetical 10% increase in the stock price at December 31, 2020 from $90.93 to $100.02 per share would have increased the expense recorded during 2020 by $2.4 million related to the stock price appreciation milestones. Keeping all other variables constant, a hypothetical 10% decrease in the stock price at December 31, 2020 from $90.93 to $81.84 per share would have decreased the expense recorded during 2020 by $2.6 million related to the stock price appreciation milestones.

The following table presents the changes in fair value of the Company’s Level 3 stock price appreciation milestones liability (in thousands):

Balance at December 31, 2019	$	—
Changes in fair value of stock price appreciation milestones liability		47,702
Balance at December 31, 2020	$	47,702

None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Convertible Preferred Stock and Stockholders' Equity

12 Months Ended

Dec. 31, 2020

Convertible Preferred Stock And Stockholders Deficit Disclosure [Abstract]

Convertible Preferred Stock and Stockholders’ Equity

9. Convertible Preferred Stock and Stockholders’ Equity

Convertible Preferred Stock

In November 2016, the Company completed a private placement of stock in which investors, including investors affiliated with the directors and officers of the Company, purchased convertible preferred stock and common stock of the Company (the November 2016 Placement). The Company issued 2,819,549 shares of non-voting Class A Convertible Preferred Stock (the Class A Preferred) at $13.30 per share, each of which is convertible into five shares of common stock upon certain conditions defined in the Certificate of Designation of Preferences, Rights and Limitations of the Class A Preferred filed with the Delaware Secretary of State on November 22, 2016 (the CoD). The Class A Preferred were purchased exclusively by entities affiliated with Redmile Group, LLC (collectively, Redmile). The terms of the CoD prohibited Redmile from converting the Class A Preferred into shares of the Company’s common stock if, as a result of conversion, Redmile, together with its affiliates, would own more than 9.99% of the Company’s common stock then issued and outstanding (the Redmile Percentage Limitation), which percentage could change at Redmile’s election upon 61 days’ notice to the Company to (i) any other number less than or equal to 19.99% or (ii) subject to approval of the Company’s stockholders to the extent required in accordance with the NASDAQ Global Market rules, any number in excess of 19.99%. On May 2, 2017, the Company’s stockholders approved the issuance of up to an aggregate of 14,097,745 shares of common stock upon the conversion of the outstanding shares of Class A Preferred. As a result, Redmile has the right to increase the Redmile Percentage Limitation to any percentage in excess of 19.99% at its election. The Company also issued 7,236,837 shares of common stock at $2.66 per share as part of the November 2016 Placement.

The Class A Preferred are non-voting shares and have a stated par value of $0.001 per share and are convertible into five shares of the Company’s common stock at a conversion price of $2.66 per share, which was the fair value of the Company’s common stock on the date of issuance. Holders of the Class A Preferred have the same dividend rights as holders of the Company’s common stock. Additionally, the liquidation preferences of the Class A Preferred are pari passu among holders of the Company’s common stock and holders of the Class A Preferred, pro rata based on the number of shares held by each such holder (treated for this purpose as if the Class A Preferred had been converted to common stock).

During the year ended December 31, 2019, 25,000 shares of the Company’s Class A Preferred were converted into 125,000 shares of the Company’s common stock.

Description of Securities

Dividends

As of December 31, 2020, the Board of Directors of the Company has not declared any dividends.

2013 Stock Option and Incentive Plan, and Inducement Equity Plan

2013 Stock Option and Incentive Plan

On August 28, 2013, the Company’s board of directors and stockholders approved and adopted the 2013 Stock Option and Incentive Plan (the 2013 Plan). The 2013 Plan became effective immediately prior to the Company’s IPO. The 2013 Plan was subsequently amended in May 2017. Under the 2013 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, directors or consultants of the Company or its subsidiaries. A total of 1,020,000 shares of common stock were initially reserved for issuance under the 2013 Plan, and in May 2017, stockholders approved an additional 2,500,000 shares of common stock for issuance under the 2013 Plan. The shares issuable pursuant to awards granted under the 2013 Plan will be authorized, but unissued shares. The shares of common stock underlying any awards from the 2013 Plan and a previously existing equity plan from 2007 that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by us prior to vesting, satisfied without any issuance of common stock, expire or are otherwise terminated (other than by exercise) will be added back to the shares of common stock available for issuance under the 2013 Plan.

In addition, the number of shares of stock available for issuance under the 2013 Plan will be automatically increased each January 1 by 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number as determined by the compensation committee of the Company’s board of directors.

Recipients of stock options under the 2013 Plan shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair value of such stock on the date of grant. Under the 2013 Plan, stock options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, or vest monthly over four years, unless they contain specific performance and/or market-based vesting provisions. The maximum term of stock options granted under the 2013 Plan is ten years. Under the 2013 Plan, restricted stock units generally vest annually over four years.

Inducement Plan

On May 10, 2016, the Company’s board of directors approved the Fate Therapeutics, Inc. Inducement Equity Plan (the Inducement Plan), the purpose of which is to enable the Company to grant equity awards to induce highly-qualified prospective officers and employees who are not employed by the Company to accept employment with the Company. Under the Inducement Plan, the Company may grant non-qualified stock options and restricted stock units. A total of 500,000 shares of common stock were initially reserved for issuance under the Inducement Plan. In March 2020, January 2019 and January 2018, an additional 470,822 shares, 200,000 shares and 400,000 shares, respectively, of common stock were reserved for issuance under the Inducement Plan. The shares of common stock underlying any awards from the Inducement Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by us prior to vesting, satisfied without any issuance of common stock, expire or are otherwise terminated (other than by exercise) under the Inducement Plan will be added back to the shares of common stock available for issuance under the Inducement Plan.

Employee Stock Purchase Plan

On September 13, 2013, the Company’s board of directors approved and adopted the 2013 Employee Stock Purchase Plan (the ESPP). A total of 729,000 shares of common stock were initially reserved for issuance under the ESPP. In addition, the number of shares of stock available for issuance under the ESPP will be automatically increased each January 1, beginning on January 1, 2015, by the lesser of (i) 2% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 450,000 shares, or (iii) such lesser number as determined by the compensation committee of the Company’s board of directors.

No purchases have been made to date under the ESPP.

Stock Options and Restricted Stock Unit Awards

Stock Options. The following table summarizes stock option activity and related information under all equity plans for the year ended December 31, 2020:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2019		9,327,742		$	9.67		7.73	$	92,567
Granted		2,756,108			29.29
Exercised		(1,419,117	)		6.76
Cancelled		(231,911	)		15.73
Outstanding at December 31, 2020		10,432,822		$	15.11		7.48	$	791,000
Options vested and expected to vest at December 31, 2020		10,432,822		$	15.11		7.48	$	791,000
Options exercisable at December 31, 2020		5,540,840		$	9.07		6.51	$	453,593

For the year ended December 31, 2020 and 2019, the weighted average grant date fair value of stock options granted per share was equal to $18.87 and $11.52, respectively. For the year ended December 31, 2018, the weighted average grant date fair value of stock options granted to employees and directors was equal to $8.28.

During the years ended December 31, 2020, 2019 and 2018, the total fair value of stock options vested was $21.0 million, $12.4 million and $5.4 million, respectively.

As of December 31, 2020, 2019 and 2018, the unrecognized compensation cost related to outstanding options was $66.1 million, $40.4 million and $15.9 million, respectively, which was expected to be recognized as expense over approximately 2.9 years, 2.9 years and 3.1 years, respectively.

The total intrinsic value, which is the amount by which the exercise price was exceeded by the price of the Company’s common stock on the date of exercise, of stock options exercised during the years ended December 31, 2020, 2019 and 2018, was $59.7 million, $10.7 million, and $5.5 million, respectively. Total cash received upon the exercise of stock options was $9.7 million for the year ended December 31, 2020.

Restricted Stock Units. The following table summarizes restricted stock unit activity and related information under all equity plans for the year ended December 31, 2020:

	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Vesting Period		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2019		520,000		$	16.41		2.64	$	10,176
Granted		1,033,323			22.86
Vested		(85,000	)		16.34
Cancelled		(66,591	)		21.94
Outstanding at December 31, 2020		1,401,732		$	20.91		2.64	$	127,459
Restricted stock units expected to vest at December 31, 2020		1,401,732		$	20.91		2.64	$	127,459

During years ended December 31, 2020, 2019 and 2018, the total fair value of restricted stock units vested was $1.9 million, $2.4 million and $0.3 million, respectively.

As of December 31, 2020, 2019 and 2018, the unrecognized compensation cost related to outstanding restricted stock units was $20.8 million, $6.2 million, and $0.4 million respectively, which was expected to be recognized as expense over approximately 2.9 years, 2.7 years, and 0.8 years respectively.

Stock-Based Compensation Expense

The allocation of stock-based compensation for all stock awards is as follows (in thousands):

	Years Ended December 31,
	2020		2019		2018
Research and development	$	18,636	$	9,804	$	3,654
General and administrative		12,117		7,606		2,639
Total stock-based compensation expense	$	30,753	$	17,410	$	6,293

Stock Option Grants Valuation. As of January 1, 2019, the Company adopted ASU 2018-07, which aligned the guidance on share-based payments to nonemployees with that for share-based payments to employees. In accordance with ASU 2018-07, the measurement of equity-classified nonemployee awards is fixed at the grant date and entities are not required to remeasure nonemployee equity awards at each reporting date until such time that the measurement date is established. The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows:

	Years Ended December 31,
	2020			2019			2018
Risk–free interest rate		1.0	%		2.4	%		2.5	%
Expected volatility		77.5	%		80.1	%		79.3	%
Expected term (in years)		5.5			6.1			6.0
Expected dividend yield		0.0	%		0.0	%		0.0	%

Risk-free interest rate. The Company bases the risk-free interest rate assumption on observed interest rates appropriate for the expected term of the stock option grants.

Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends.

Expected volatility. During the year ended December 31, 2020, the Company based the expected volatility on the historical volatility of its common stock over the most recent period commensurate with the estimated expected term of the Company’s stock options, as the Company determined there was sufficient operating history and company-specific historical volatility to estimate the expected volatility. During the years ended December 31, 2019 and 2018, the expected volatility assumption was based on historical volatilities of a peer group of similar companies whose share prices were publicly available. The peer group was developed based on companies in the biotechnology industry.

Expected term. The expected term represents the period of time that options are expected to be outstanding. During the year ended December 31, 2020, the Company estimated the expected term using historical experience and anticipated future exercise behavior. During the years ended December 31, 2019 and 2018, due to limited historical exercise behavior, the Company determined the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance is as follows:

	December 31,
	2020		2019
Convertible preferred stock (if converted)		13,972,745		13,972,745
Common stock options		10,432,822		9,327,742
Restricted stock units		1,401,732		520,000
Awards available under the 2013 Plan		2,618,516		2,880,235
Awards available under the Inducement Plan		550,000		279,178
Employee stock purchase plan		729,000		729,000
Total		29,704,815		27,708,900

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The following is a reconciliation of the Company’s expected federal income tax provision (benefit) to the actual income tax provision (in thousands):

	Years Ended December 31,
	2020			2019			2018
Tax computed at federal statutory rate	$	(36,411	)	$	(20,611	)	$	(13,985	)
State tax, net of federal tax benefit		(1,296	)		(2,088	)		(1,620	)
Permanent differences		(165	)		175			22
Stock compensation		(6,073	)		359			(307	)
R&D tax credits		(7,177	)		(7,285	)		(3,301	)
Reserve for uncertain tax positions		1,555			2,163			1,160
Other		70			77			304
Valuation allowance		49,497			27,210			17,727
Income tax expense	$	—		$	—		$	—

Significant components of the Company’s deferred tax assets are summarized as follows (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Section 59e amortization	$	48,195		$	32,781
Net operating losses		41,213			37,563
R&D tax credits		23,488			16,391
Intangible asset amortization		2,615			1,650
Deferred revenue		11,915			2,115
Stock compensation		4,307			2,346
Lease liability		20,433			5,655
Other		10,208			846
Total deferred tax assets		162,374			99,347
Deferred tax liabilities:
Depreciation		(4,220	)		—
Right-of-use assets		(14,088	)		(4,778	)
Total deferred tax liabilities		(18,308	)		(4,778	)
Net of deferred tax assets and liabilities		144,066			94,569
Valuation allowance		(144,066	)		(94,569	)
Net deferred tax assets	$	—		$	—

A valuation allowance of $144.1 million and $94.6 million at December 31, 2020 and 2019, respectively, has been established to offset the deferred tax assets, as realization of such assets is uncertain.

At December 31, 2020, the Company had federal and California net operating loss (NOL) carryforwards of $186.4 million and $188.0 million, respectively, which may be available to offset future taxable income. Of the federal NOLs, $67.0 million are indefinite lived and are limited to offsetting eighty-percent of taxable income within a fiscal year. The remaining federal and California NOL carryforwards begin to expire in 2027 and 2028, respectively, unless previously utilized. At December 31, 2020, the Company had federal and California research and development (R&D) credit carryforwards of $18.0 million and $12.9 million, respectively. The federal R&D tax credit carryforwards will begin to expire in 2035 unless previously utilized. The California R&D credit carryforwards will carry forward indefinitely.

Under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended, (the Code), substantial changes in the Company’s ownership may limit the amount of net operating loss and research and development credit carryforwards that could be used annually in the future to offset taxable income. The tax benefits related to future utilization of federal and state net operating loss carryforwards, credit carryforwards, and other deferred tax assets may be limited or lost if cumulative changes in ownership exceeds 50% within any three-year period. The Company had previously completed a study to assess whether an ownership change, as defined by Section 382 of the Code, had occurred from the Company’s formation through December 31, 2015. Based upon this study, the Company determined that several ownership changes had occurred. Accordingly, the Company reduced its deferred tax assets related to the federal NOL carryforwards and the federal R&D credit carryforwards that are anticipated to expire unused as a result of these ownership changes. These tax attributes were excluded from deferred tax assets with a corresponding reduction of the valuation allowance with no net effect on income tax expense or the effective tax rate. The Company updated the study through December 31, 2020 and concluded there were no ownership changes subsequent to December 31, 2015. Future ownership changes may further limit the Company’s ability to utilize its remaining tax attributes.

The Company files income tax returns in the United States and California and has historically filed income tax returns in Canada. The Company currently has no years under examination by any jurisdiction; however, the Company is subject to income tax examination by federal and California tax authorities for years beginning in 2017 and 2016, respectively. However, to the extent allowed by law, the taxing authorities may have the right to examine prior periods where NOLs and tax credits were generated and carried forward, and make adjustments up to the amount of the carryforwards.

The change in the Company’s unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2020		2019		2018
Beginning unrecognized tax benefits	$	16,822	$	13,547	$	11,800
Increase related to current year tax positions		1,837		3,196		1,798
Increase related to prior year tax positions		1,120		79		148
Decrease related to prior year tax positions		—		—		(199	)
Ending unrecognized tax benefits	$	19,779	$	16,822	$	13,547

The Company does not anticipate that the amount of unrecognized tax benefits as of December 31, 2020 will significantly change within the next twelve months. Due to the valuation allowance recorded against the Company’s deferred tax assets, none of the total unrecognized tax benefits as of December 31, 2020 would reduce the effective tax rate if recognized. The Company has not recognized interest or penalties related to income tax matters in its consolidated statements of operations and comprehensive loss since inception.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Organization and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Public Equity Offering

Public Equity Offerings

Private Placements of Common Stock

Use of Estimates

Risks and Uncertainties

Principles of Consolidation

Segment Reporting

Fair Value of Financial Instruments

Level 1: Observable inputs such as quoted prices in active markets;

Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Cash, Cash Equivalents and Restricted Cash

	Years Ended December 31,
	2020		2019		2018
Cash and cash equivalents	$	167,347	$	99,814	$	190,514
Restricted cash		15,227		227		227
Total cash, cash equivalents, and restricted cash shown in the consolidated statement of cash flows	$	182,574	$	100,041	$	190,741

Investments

Concentration of Credit Risk

Property and Equipment

Impairment of Long-Lived Assets

Leases

Revenue Recognition

Stock Price Appreciation Milestones

Research and Development Costs

All research and development costs are expensed as incurred.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.

Stock-Based Compensation

Convertible Preferred Stock

Income Taxes

Comprehensive Loss

Net Loss Per Common Share

Potentially dilutive securities are not included in the calculation of diluted net loss per common share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):

	As of December 31,
	2020		2019		2018
Warrants for common stock		—		—		85,094
Common stock options		10,432,822		9,327,742		6,980,581
Restricted stock units		1,401,732		520,000		188,625
Series A convertible preferred stock (if converted)		13,972,745		13,972,745		14,097,745
Total		25,807,299		23,820,487		21,352,045

Going Concern Assessment

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issues Accounting Pronouncements

Investments (Tables)

12 Months Ended

Dec. 31, 2020

Investments [Abstract]

Summary of Investments

The following table summarizes the Company’s investments accounted for as available-for-sale securities as of December 31, 2020 and 2019 (in thousands):

	Maturity (in years)	Amortized Cost		Unrealized Losses			Unrealized Gains		Estimated Fair Value
December 31, 2020
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	39,736	$	—		$	31	$	39,767
Non-U.S. government securities	1 or less		5,054		—			2	$	5,056
Municipal securities	1 or less		3,082		(1	)		—	$	3,081
Corporate debt securities	1 or less		159,947		(68	)		124	$	160,003
Commercial paper	1 or less		107,680		(18	)		—	$	107,662
Total short-term investments		$	315,499	$	(87	)	$	157	$	315,569

December 31, 2019
Classified as current assets:
U.S. Treasury debt securities	1 or less	$	50,445	$	(4	)	$	16	$	50,457
Corporate debt securities	1 or less		71,171		(24	)		9		71,156
Total short-term investments		$	121,616	$	(28	)	$	25	$	121,613
Classified as non-current assets:
U.S. Treasury debt securities	Greater than 1	$	9,841	$	—		$	5	$	9,846
Corporate debt securities	Greater than 1		29,572		(1	)		23		29,594
Total long-term investments		$	39,413	$	(1	)	$	28	$	39,440

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

The following tables presents the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2020 and 2019 (in thousands):

			Fair Value Measurements at Reporting Date Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020:
Financial assets:
Money market funds	$	167,347	$	167,347	$	—	$	—
U.S. Treasury debt securities		39,767		39,767		—		—
Non-U.S. government securities		5,056		—		5,056		—
Municipal securities		3,081		—		3,081		—
Corporate debt securities		160,003		—		160,003		—
Commercial paper		107,662		—		107,662		—
Total assets measured at fair value on a recurring basis	$	482,916	$	207,114	$	275,802	$	—

Financial liabilities:
Stock price appreciation milestones	$	47,702	$	—	$	—	$	47,702
Total financial liabilities measured at fair value on a recurring basis	$	47,702	$	—	$	—	$	47,702

As of December 31, 2019:
Financial assets:
Money market funds	$	84,814	$	84,814	$	—	$	—
U.S. Treasury debt securities		60,303		60,303		—		—
Corporate debt securities		100,750		—		100,750		—
Total financial assets measured at fair value on a recurring basis	$	245,867	$	145,117	$	100,750	$	—

Summary of Changes in the Fair Value of the Company’s Level 3 Enterprise Fair Value Milestone Payment Liability

The following table presents the changes in fair value of the Company’s Level 3 stock price appreciation milestones liability (in thousands):

Balance at December 31, 2019	$	—
Changes in fair value of stock price appreciation milestones liability		47,702
Balance at December 31, 2020	$	47,702

Convertible Preferred Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2020

Stockholders' Equity

Summary of stock option activity and related information under all equity plans

The following table summarizes stock option activity and related information under all equity plans for the year ended December 31, 2020:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2019		9,327,742		$	9.67		7.73	$	92,567
Granted		2,756,108			29.29
Exercised		(1,419,117	)		6.76
Cancelled		(231,911	)		15.73
Outstanding at December 31, 2020		10,432,822		$	15.11		7.48	$	791,000
Options vested and expected to vest at December 31, 2020		10,432,822		$	15.11		7.48	$	791,000
Options exercisable at December 31, 2020		5,540,840		$	9.07		6.51	$	453,593

Summary of restricted stock unit activity and related information under all equity plans

The following table summarizes restricted stock unit activity and related information under all equity plans for the year ended December 31, 2020:

	Number of Restricted Stock Units			Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Vesting Period		Aggregate Intrinsic Value (in 000s)
Outstanding at December 31, 2019		520,000		$	16.41		2.64	$	10,176
Granted		1,033,323			22.86
Vested		(85,000	)		16.34
Cancelled		(66,591	)		21.94
Outstanding at December 31, 2020		1,401,732		$	20.91		2.64	$	127,459
Restricted stock units expected to vest at December 31, 2020		1,401,732		$	20.91		2.64	$	127,459

Schedule of weighted-average assumptions used to determine the fair value of employee and nonemployee stock option grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows

	Years Ended December 31,
	2020			2019			2018
Risk–free interest rate		1.0	%		2.4	%		2.5	%
Expected volatility		77.5	%		80.1	%		79.3	%
Expected term (in years)		5.5			6.1			6.0
Expected dividend yield		0.0	%		0.0	%		0.0	%

Schedule of common stock reserved for future issuance

Common stock reserved for future issuance is as follows:

	December 31,
	2020		2019
Convertible preferred stock (if converted)		13,972,745		13,972,745
Common stock options		10,432,822		9,327,742
Restricted stock units		1,401,732		520,000
Awards available under the 2013 Plan		2,618,516		2,880,235
Awards available under the Inducement Plan		550,000		279,178
Employee stock purchase plan		729,000		729,000
Total		29,704,815		27,708,900

Stock Option And Incentive Plan 2013

Stockholders' Equity

Schedule of allocation of stock-based compensation for all stock awards

The allocation of stock-based compensation for all stock awards is as follows (in thousands):

	Years Ended December 31,
	2020		2019		2018
Research and development	$	18,636	$	9,804	$	3,654
General and administrative		12,117		7,606		2,639
Total stock-based compensation expense	$	30,753	$	17,410	$	6,293

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of reconciliation of the Company's expected federal income tax provision (benefit) to the actual income tax provision

The following is a reconciliation of the Company’s expected federal income tax provision (benefit) to the actual income tax provision (in thousands):

	Years Ended December 31,
	2020			2019			2018
Tax computed at federal statutory rate	$	(36,411	)	$	(20,611	)	$	(13,985	)
State tax, net of federal tax benefit		(1,296	)		(2,088	)		(1,620	)
Permanent differences		(165	)		175			22
Stock compensation		(6,073	)		359			(307	)
R&D tax credits		(7,177	)		(7,285	)		(3,301	)
Reserve for uncertain tax positions		1,555			2,163			1,160
Other		70			77			304
Valuation allowance		49,497			27,210			17,727
Income tax expense	$	—		$	—		$	—

Summary of significant components of the Company's deferred tax assets

Significant components of the Company’s deferred tax assets are summarized as follows (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Section 59e amortization	$	48,195		$	32,781
Net operating losses		41,213			37,563
R&D tax credits		23,488			16,391
Intangible asset amortization		2,615			1,650
Deferred revenue		11,915			2,115
Stock compensation		4,307			2,346
Lease liability		20,433			5,655
Other		10,208			846
Total deferred tax assets		162,374			99,347
Deferred tax liabilities:
Depreciation		(4,220	)		—
Right-of-use assets		(14,088	)		(4,778	)
Total deferred tax liabilities		(18,308	)		(4,778	)
Net of deferred tax assets and liabilities		144,066			94,569
Valuation allowance		(144,066	)		(94,569	)
Net deferred tax assets	$	—		$	—

Summary of the change in the Company's unrecognized tax benefits

The change in the Company’s unrecognized tax benefits is summarized as follows (in thousands):

	December 31,
	2020		2019		2018
Beginning unrecognized tax benefits	$	16,822	$	13,547	$	11,800
Increase related to current year tax positions		1,837		3,196		1,798
Increase related to prior year tax positions		1,120		79		148
Decrease related to prior year tax positions		—		—		(199	)
Ending unrecognized tax benefits	$	19,779	$	16,822	$	13,547

Organization and Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) segment shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Jan. 31, 2020 USD ($)
Organization and summary of significant accounting policies
Aggregate purchase price of common stock					$ 188,784	$ 162,406	$ 134,791
Aggregate purchase price of common stock					$ 188,784	162,406	134,791
Number of operating segments \| segment					1
Number of reportable segments \| segment					1
Letters of credit outstanding amount					$ 15,200	$ 200	$ 200
Maximum
Organization and summary of significant accounting policies
Short-term leases term excluded from calculation of ROU and lease liabilities					12 months
Common Stock
Organization and summary of significant accounting policies
Public offerings of common stock, net of offering costs (in shares) \| shares					7,108,796	9,890,000	10,648,149
Aggregate purchase price of common stock					$ 7	$ 10	$ 11
Aggregate purchase price of common stock					$ 7	$ 10	$ 11
Silicon Valley Bank \| Letter of Credit
Organization and summary of significant accounting policies
Letters of credit outstanding amount								$ 15,000
June 2020 Public Offering
Organization and summary of significant accounting policies
Public offerings of common stock, net of offering costs (in shares) \| shares	7,100,000
Share issue price (in dollars per share) \| $ / shares	$ 28.31
Aggregate purchase price of common stock	$ 201,300
Net proceeds from issuance of shares after related cash costs	188,800
Costs related to equity offering	12,500
Aggregate purchase price of common stock	$ 201,300
Share issue price (in dollars per share) \| $ / shares	$ 28.31
Net proceeds from issuance of shares after related cash costs	$ 188,800
September 2019 Public Equity Offering
Organization and summary of significant accounting policies
Public offerings of common stock, net of offering costs (in shares) \| shares			9,900,000
Share issue price (in dollars per share) \| $ / shares			$ 17.50
Aggregate purchase price of common stock			$ 173,100
Net proceeds from issuance of shares after related cash costs			162,400
Costs related to equity offering			10,700
Aggregate purchase price of common stock			$ 173,100
Share issue price (in dollars per share) \| $ / shares			$ 17.50
Net proceeds from issuance of shares after related cash costs			$ 162,400
September 2018 Public Equity Offering
Organization and summary of significant accounting policies
Public offerings of common stock, net of offering costs (in shares) \| shares				10,600,000
Share issue price (in dollars per share) \| $ / shares				$ 13.50
Aggregate purchase price of common stock				$ 143,800
Net proceeds from issuance of shares after related cash costs				134,900
Costs related to equity offering				8,900
Aggregate purchase price of common stock				$ 143,800
Share issue price (in dollars per share) \| $ / shares				$ 13.50
Net proceeds from issuance of shares after related cash costs				$ 134,900
Private Placement \| Johnson Johnson Innovation J J D C Inc \| Common Stock
Organization and summary of significant accounting policies
Share issue price (in dollars per share) \| $ / shares	$ 28.31
Aggregate purchase price of common stock	$ 50,000
Net proceeds from issuance of shares after related cash costs	50,000
Aggregate purchase price of common stock	$ 50,000
Issuance of common stock during period for private placements (in shares) \| shares	1,800,000
Share issue price (in dollars per share) \| $ / shares	$ 28.31
Net proceeds from issuance of shares after related cash costs	$ 50,000
Private Placement \| Stock Purchase Agreement \| Johnson Johnson Innovation J J D C Inc \| Common Stock
Organization and summary of significant accounting policies
Share issue price (in dollars per share) \| $ / shares		$ 31.00
Net proceeds from issuance of shares after related cash costs		$ 50,000
Issuance of common stock during period for private placements (in shares) \| shares		1,600,000
Share issue price (in dollars per share) \| $ / shares		$ 31.00
Net proceeds from issuance of shares after related cash costs		$ 50,000

Collaboration and License Agreements (Details) - USD ($)							1 Months Ended		12 Months Ended
	Apr. 07, 2020	Apr. 02, 2020	May 04, 2019	Sep. 14, 2018	Sep. 11, 2018	May 15, 2018	Jun. 30, 2020	Oct. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 04, 2020	May 31, 2019
Collaboration agreement
Aggregate purchase price of common stock									$ 188,784,000	$ 162,406,000	$ 134,791,000
Proceeds from private placement of common stock, net of issuance costs									49,975,000
Collaboration contract asset									13,506,000	1,338,000
Revenue recognized									$ 31,434,000	$ 10,680,000	4,740,000
Common stock issued									87,722,237	75,730,260
Research and development									$ 125,623,000	$ 87,770,000	56,024,000
Issuance of common stock for license agreements											6,100,000
First Janssen Cancer Target \| Maximum \| Janssen Agreement
Collaboration agreement
Development, regulatory, and sales milestones	$ 898,000,000.0
Additional candidate milestone Payments	460,000,000.0
Additional Cancer Targets \| Maximum \| Janssen Agreement
Collaboration agreement
Development, regulatory, and sales milestones	706,000,000.0
Additional candidate milestone Payments	$ 340,000,000.0
Johnson Johnson Innovation J J D C Inc \| Stock Purchase Agreement
Collaboration agreement
Issuance of common stock during period for private placements (in shares)		1,600,000
Common stock per share		$ 31.00
Aggregate purchase price of common stock		$ 50,000,000.0
Equity premium per share		$ 9.93
Aggregate equity premium on shares		$ 16,000,000.0
Proceeds from private placement of common stock, net of issuance costs		34,000,000.0
Johnson Johnson Innovation J J D C Inc \| Stock Purchase Agreement \| Private Placement
Collaboration agreement
Issuance of common stock during period for private placements (in shares)							1,800,000
Proceeds from private placement of common stock, net of issuance costs							$ 50,000,000.0
Aggregate value of common stock							$ 50,000,000.0
Share issue price (in dollars per share)									$ 28.31
Janssen Biotech Inc
Collaboration agreement
Upfront, non-refundable and non-creditable payment		50,000,000.0							$ 50,000,000.0
Transaction price of the agreement		66,000,000.0
Equity premium		16,000,000.0
Non-refundable upfront payments recorded as deferred revenue		66,000,000.0
Collaboration contract asset		$ 13,300,000							12,000,000.0
Amortization of sublicense consideration									1,300,000
Revenue recognized									16,800,000
Deferred revenue									59,500,000
Deferred revenue classified as current									16,300,000
Research and development fees cash payments received									4,800,000
Janssen Biotech Inc \| Research And Development
Collaboration agreement
Revenue recognized									10,300,000
Janssen Biotech Inc \| Upfront Fee and Equity Premium
Collaboration agreement
Revenue recognized									6,500,000
Ono Pharmaceutical Company Ltd
Collaboration agreement
Transaction price of the agreement				$ 30,000,000.0
Non-refundable upfront payments recorded as deferred revenue				10,000,000.0
Collaboration contract asset												$ 4,000,000.0
Amortization of sublicense consideration									1,800,000	600,000
Revenue recognized									14,600,000	9,300,000	600,000
Deferred revenue									7,700,000
Deferred revenue classified as current									4,800,000
Research and development fees cash payments received									12,300,000
Aggregate research and development fees payments receivable				20,000,000.0
Collaborative arrangement potential additional milestones				$ 20,000,000.0
Expected ressarch services period				4 years
Payments for research and development fees								$ 5,000,000.0
Non-refundable upfront payments recorded as deferred revenue				$ 10,000,000.0
Collaborative arrangement annual payments receivable recorded as deferred revenue				$ 12,300,000				$ 5,000,000.0
Ono Pharmaceutical Company Ltd \| Candidate 2
Collaboration agreement
Percentage of reduction on milestone payments				50.00%
Ono Pharmaceutical Company Ltd \| Collaborative Arrangement \| Research services
Collaboration agreement
Revenue recognized									5,700,000	6,200,000	400,000
Ono Pharmaceutical Company Ltd \| Collaborative Arrangement \| Upfront Fee
Collaboration agreement
Revenue recognized									2,800,000	3,100,000	200,000
Ono Pharmaceutical Company Ltd \| Maximum \| Candidate 2
Collaboration agreement
Aggregate milestone payments				$ 885,000,000.0
Ono Pharmaceutical Company Ltd \| Minimum \| Collaborative Arrangement
Collaboration agreement
Profits and losses sharing percentage				50.00%
Ono Pharmaceutical Company Ltd \| Ono Letter Agreement
Collaboration agreement
Revenue recognized									6,100,000
Milestone payments												10,000,000.0
Milestone payments recorded to deferred revenue												$ 10,000,000.0
Ono Pharmaceutical Company Ltd \| Ono Letter Agreement \| Sublicense Consideration
Collaboration agreement
Collaboration contract asset									1,500,000
Sublicense consideration paid									4,000,000.0
Juno Therapeutics, Inc \| Collaborative Arrangement
Collaboration agreement
Revenue recognized									0	1,400,000	4,100,000
Research term			4 years
Collaboration agreement expiration date			May 04, 2015
Agreement to terminate upon the receipt of research payment													$ 200,000
Juno Therapeutics, Inc \| Collaborative Arrangement \| Upfront Fee and Equity Premium
Collaboration agreement
Revenue recognized										700,000	2,100,000
Juno Therapeutics, Inc \| Collaborative Arrangement \| Research services
Collaboration agreement
Revenue recognized										$ 700,000	$ 2,000,000.0
MSK \| Amended MSK License
Collaboration agreement
Common stock issued						500,000
Research and development						$ 5,300,000
Upfront cash payment						500,000
Issuance of common stock for license agreements						$ 4,800,000
Amended MSK License
Collaboration agreement
Stock price appreciation milestones potential payments									75,000,000.0
Stock price appreciation milestone, expense									47,700,000
Stock price appreciation milestone, liability									$ 47,700,000
Gladstone \| Gladstone License Agreement
Collaboration agreement
Aggregate milestone payments					$ 1,900,000
Common stock issued					100,000
Research and development					$ 1,400,000
Upfront cash payment					100,000
Issuance of common stock for license agreements					$ 1,300,000

Convertible Preferred Stock and Stockholders' Equity (Details) - USD ($)		1 Months Ended	12 Months Ended				88 Months Ended
	Sep. 13, 2013	Nov. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2020	Mar. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	May 31, 2017	May 02, 2017	May 10, 2016	Aug. 28, 2013
Convertible preferred stock
Preferred stock, par value (in dollars per share)			$ 0.001	$ 0.001			$ 0.001
Dividends declared			$ 0
Shares reserved for issuance			29,704,815	27,708,900			29,704,815
Stock purchases under the plan (in shares)							0
Issuance of common stock from equity incentive plans, net of issuance costs			$ 9,655,000	$ 2,522,000	$ 2,693,000
Employee And Non Employee Stock Option
Convertible preferred stock
Total intrinsic value of stock options exercised			59,700,000	$ 10,700,000	5,500,000
Issuance of common stock from equity incentive plans, net of issuance costs			$ 9,700,000
Employee Stock
Convertible preferred stock
Shares reserved for issuance	729,000		729,000	729,000			729,000
Additional shares authorized (as a percent)	2.00%
Additional shares authorized	450,000
Restricted Stock Units (RSUs)
Convertible preferred stock
Shares reserved for issuance			1,401,732	520,000			1,401,732
Total fair value of stock options vested				$ 1,900,000	$ 2,400,000	$ 300,000
Expected recognition period of unrecognized compensation cost				2 years 10 months 24 days	2 years 8 months 12 days	9 months 18 days
Unrecognized compensation cost related to unvested restricted shares				$ 20,800,000	$ 6,200,000	$ 400,000
Stock Option And Incentive Plan 2013
Convertible preferred stock
Shares reserved for issuance											2,500,000			1,020,000
Additional shares authorized (as a percent)														4.00%
Total fair value of stock options vested			$ 21,000,000.0	$ 12,400,000	5,400,000
Stock Option And Incentive Plan 2013 \| Employee And Non Employee Stock Option
Convertible preferred stock
Stock options generally vested on anniversary grant date (as a percent)			25.00%
General vesting period after first year			3 years
Monthly vesting period			4 years
Term of stock awards			10 years
Annually vesting period			4 years
Weighted-average grant date fair value per share of employee options granted			$ 18.87	$ 11.52
Unrecognized compensation cost related to outstanding options			$ 66,100,000	$ 40,400,000	$ 15,900,000		$ 66,100,000
Expected recognition period of unrecognized compensation cost			2 years 10 months 24 days	2 years 10 months 24 days	3 years 1 month 6 days
Stock Option And Incentive Plan 2013 \| Employee and Directors Stock Option
Convertible preferred stock
Weighted-average grant date fair value per share of employee options granted					$ 8.28
Inducement Plan
Convertible preferred stock
Shares reserved for issuance			550,000	279,178			550,000						500,000
Additional shares reserved for issuance								470,822	200,000	400,000
Common Stock
Convertible preferred stock
Common stock issued			7,108,796	9,890,000	10,648,149
Conversion of preferred shares to common stock				125,000
Non-Voting Class A Preferred Stock \| Redmile Group, LLC and Affiliates
Convertible preferred stock
Terms of conversion			The Class A Preferred were purchased exclusively by entities affiliated with Redmile Group, LLC (collectively, Redmile). The terms of the CoD prohibited Redmile from converting the Class A Preferred into shares of the Company’s common stock if, as a result of conversion, Redmile, together with its affiliates, would own more than 9.99% of the Company’s common stock then issued and outstanding (the Redmile Percentage Limitation), which percentage could change at Redmile’s election upon 61 days’ notice to the Company to (i) any other number less than or equal to 19.99% or (ii) subject to approval of the Company’s stockholders to the extent required in accordance with the NASDAQ Global Market rules, any number in excess of 19.99%. On May 2, 2017, the Company’s stockholders approved the issuance of up to an aggregate of 14,097,745 shares of common stock upon the conversion of the outstanding shares of Class A Preferred. As a result, Redmile has the right to increase the Redmile Percentage Limitation to any percentage in excess of 19.99% at its election.
Non-Voting Class A Preferred Stock \| Maximum
Convertible preferred stock
Number of shares to be issued upon conversion												14,097,745
Non-Voting Class A Preferred Stock \| Maximum \| Redmile Group, LLC and Affiliates
Convertible preferred stock
Percentage of common stock ownership upon preferred stock conversion		9.99%
Preferred shares converted into common stock percentage of ownership change upon notice		19.99%
Class A Convertible Preferred Shares
Convertible preferred stock
Preferred stock, issued shares			2,794,549	2,794,549			2,794,549
Conversion of preferred shares to common stock				(25,000)
November 2016 Placement \| Common Stock
Convertible preferred stock
Share issue price (in dollars per share)		$ 2.66
Common stock issued		7,236,837
November 2016 Placement \| Non-Voting Class A Preferred Stock
Convertible preferred stock
Preferred stock, issued shares		2,819,549
Share issue price (in dollars per share)		$ 13.30
Number of shares to be issued upon conversion		5
Preferred stock, par value (in dollars per share)		$ 0.001
Conversion price		$ 2.66

Convertible Preferred Stock and Stockholders' Equity (Details 2) - Stock Option And Incentive Plan 2013 - Employee And Non Employee Stock Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Balance at the beginning of the period	9,327,742
Granted	2,756,108
Exercised	(1,419,117)
Cancelled	(231,911)
Balance at the end of the period	10,432,822	9,327,742
Vested and expected to vest at the end of the period	10,432,822
Exercisable at the end of the period	5,540,840
Weighted-Average Price
Balance at the beginning of the period	$ 9.67
Granted	29.29
Exercised	6.76
Cancelled	15.73
Balance at the end of the period	15.11	$ 9.67
Vested and expected to vest at the end of the period	15.11
Exercisable at the end of the period	$ 9.07
Weighted Average Remaining Contractual Term
Outstanding at the end of the period	7 years 5 months 23 days	7 years 8 months 23 days
Vested and expected to vest at the end of the period	7 years 5 months 23 days
Exercisable at the end of the period	6 years 6 months 3 days
Aggregate Intrinsic Value
Outstanding at the end of the period	$ 791,000	$ 92,567
Vested and expected to vest at the end of the period	791,000
Exercisable at the end of the period	$ 453,593

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the Company's expected federal income tax provision (benefit) to the actual income tax provision
Tax computed at federal statutory rate	$ (36,411)	$ (20,611)	$ (13,985)
State tax, net of federal tax benefit	(1,296)	(2,088)	(1,620)
Permanent differences	(165)	175	22
Stock compensation	(6,073)	359	(307)
R&D tax credits	(7,177)	(7,285)	(3,301)
Reserve for uncertain tax positions	1,555	2,163	1,160
Other	70	77	304
Valuation allowance	49,497	27,210	$ 17,727
Deferred tax assets:
Section 59e amortization	48,195	32,781
Net operating losses	41,213	37,563
R&D tax credits	23,488	16,391
Intangible asset amortization	2,615	1,650
Deferred revenue	11,915	2,115
Stock compensation	4,307	2,346
Lease liability	20,433	5,655
Other	10,208	846
Total deferred tax assets	162,374	99,347
Deferred tax liabilities:
Depreciation	(4,220)
Right-of-use assets	(14,088)	(4,778)
Total deferred tax liabilities	(18,308)	(4,778)
Net of deferred tax assets and liabilities	144,066	94,569
Valuation allowance	$ (144,066)	$ (94,569)

Organization and Summary of Significant Accounting Policies (Details 2)	12 Months Ended
	Dec. 31, 2020
Furniture And Fixtures \| Minimum
Property and equipment
Estimated useful lives	2 years
Furniture And Fixtures \| Maximum
Property and equipment
Estimated useful lives	5 years
Computer Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Computer Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Scientific Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Scientific Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Office Equipment \| Minimum
Property and equipment
Estimated useful lives	2 years
Office Equipment \| Maximum
Property and equipment
Estimated useful lives	5 years
Construction-in-Process \| Minimum
Property and equipment
Estimated useful lives	2 years
Construction-in-Process \| Maximum
Property and equipment
Estimated useful lives	5 years

California Institute For Regenerative Medicine Award (Details) $ in Millions		12 Months Ended
	Apr. 05, 2018 USD ($) Disbursement	Dec. 31, 2020 USD ($)
Award from California institute for regenerative medicine
Period to treat award as grant, if award not treated as loan		10 years
California Institute for Regenerative Medicine
Award from California institute for regenerative medicine
Receipt of first disbursement under the Award \| $		$ 4.0
California Institute for Regenerative Medicine \| LIBOR
Award from California institute for regenerative medicine
Award considered as a loan, interest rate	7.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate One
Award from California institute for regenerative medicine
Repayment percentage of award amount	60.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Two
Award from California institute for regenerative medicine
Repayment percentage of award amount	80.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Three
Award from California institute for regenerative medicine
Repayment percentage of award amount	100.00%
California Institute for Regenerative Medicine \| Loan Repayment Rate Four
Award from California institute for regenerative medicine
Repayment percentage of award amount	100.00%
California Institute for Regenerative Medicine \| FT516
Award from California institute for regenerative medicine
Award agreement executed date	Apr. 05, 2018
Award for first-in-human clinical trial \| $	$ 4.0
Number of disbursements	5
Number of disbursement receivable upon the execution of the award	1
Number of disbursements receivable based on completion of certain operating milestones	4

Investments (Details) - USD ($)	12 Months Ended
Investments (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale securities, impairment	$ 0	$ 0	$ 0
Available-for-sale securities, realized gains (losses) on sales	0	0	0
Available-for-sale securities, recognition of expected credit losses	0	0	$ 0
Prepaid Expenses And Other Assets
Schedule Of Available For Sale Securities [Line Items]
Accured Interest on investments	$ 1,500,000	$ 1,000,000.0
Treasuries, Commercial paper. Non US government securities and Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short term investments, maturity start range	3 months
Short term investments, maturity end range	18 months

Fair Value Measurements (Details 2)	12 Months Ended
Fair Value Measurements (Details 2)	Dec. 31, 2020 USD ($) $ / shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Closing stock price as of measurement date \| $ / shares	$ 90.93
Change in fair value of stock price appreciation milestones	$ 47,702,000
Transfer of assets from level 1 to level 2	0
Transfer of assets from level 2 to level 1	0
Transfer of liabilities from level 1 to level 2	0
Transfer of liabilities from level 2 to level 1	0
Fair Value Measurements Nonrecurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets/ Non-financial assets	0
Total financial liabilities measured at fair value on a recurring basis	$ 0
Stock price increased by 10% per share
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Sensitivity analysis fair value inputs stock price increase/decrease	10.00%
Sensitivity analysis share price fair value input \| $ / shares	$ 100.02
Change in fair value of stock price appreciation milestones	$ 2,400,000
Stock price decreased by 10% per share
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Sensitivity analysis fair value inputs stock price increase/decrease	10.00%
Sensitivity analysis share price fair value input \| $ / shares	$ 81.84
Change in fair value of stock price appreciation milestones	$ 2,600,000

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and equipment
Property and equipment, gross	$ 43,403	$ 19,937
Less accumulated depreciation and amortization	(11,095)	(8,518)
Total property and equipment, net	32,308	11,419
Depreciation expense	3,087	2,193	$ 1,204
Furniture And Fixtures
Property and equipment
Property and equipment, gross	803	899
Computer And Office Equipment
Property and equipment
Property and equipment, gross	656	917
Software And Software Development Costs
Property and equipment
Property and equipment, gross	257	103
Leasehold Improvements
Property and equipment
Property and equipment, gross	2,701	2,465
Scientific Equipment
Property and equipment
Property and equipment, gross	20,794	15,355
Construction-in-Process
Property and equipment
Property and equipment, gross	$ 18,192	$ 198

Collaboration and License Agreements (Details 1) - Amended MSK License $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares
Milestone One
Collaboration agreement
Common stock multiple	5.0x
Ten-trading day trailing average common stock price \| $ / shares	$ 50.18
Stock price appreciation milestone payment \| $	$ 20.0
Milestone Two
Collaboration agreement
Common stock multiple	10.0x
Ten-trading day trailing average common stock price \| $ / shares	$ 100.36
Stock price appreciation milestone payment \| $	$ 30.0
Milestone Three
Collaboration agreement
Common stock multiple	15.0x
Ten-trading day trailing average common stock price \| $ / shares	$ 150.54
Stock price appreciation milestone payment \| $	$ 25.0

Collaboration and License Agreements (Details 2)	12 Months Ended
Collaboration and License Agreements (Details 2)	Dec. 31, 2020 $ / shares
Determine the estimated fair value of the enterprise value milestone payments
Closing stock price as of measurement date	$ 90.93
Amended MSK License
Determine the estimated fair value of the enterprise value milestone payments
Risk-free interest rate	1.50%
Expected volatility	78.10%
Estimated term (in years)	18 years
Closing stock price as of measurement date	$ 90.93

Investments (Details 2) - USD ($) $ in Thousands	12 Months Ended
Investments (Details 2) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 315,499	$ 121,616
Unrealized Losses	(87)	(28)
Unrealized Gains	157	25
Estimated Fair Value	$ 315,569	121,613
Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		39,413
Unrealized Losses		(1)
Unrealized Gains		28
Estimated Fair Value		$ 39,440
U.S. Treasury debt securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less	1 or less
Amortized Cost	$ 39,736	$ 50,445
Unrealized Losses		(4)
Unrealized Gains	31	16
Estimated Fair Value	$ 39,767	$ 50,457
U.S. Treasury debt securities \| Non-current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)		Greater than 1
Amortized Cost		$ 9,841
Unrealized Gains		5
Estimated Fair Value		$ 9,846
Non-U.S. government securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less
Amortized Cost	$ 5,054
Unrealized Gains	2
Estimated Fair Value	$ 5,056
Municipal securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less
Amortized Cost	$ 3,082
Unrealized Losses	(1)
Estimated Fair Value	$ 3,081
Corporate debt securities \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less	1 or less
Amortized Cost	$ 159,947	$ 71,171
Unrealized Losses	(68)	(24)
Unrealized Gains	124	9
Estimated Fair Value	$ 160,003	$ 71,156
Corporate debt securities \| Non-current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)		Greater than 1
Amortized Cost		$ 29,572
Unrealized Losses		(1)
Unrealized Gains		23
Estimated Fair Value		$ 29,594
Commercial Paper \| Current Assets [Member]
Schedule Of Available For Sale Securities [Line Items]
Maturity (in years)	1 or less
Amortized Cost	$ 107,680
Unrealized Losses	(18)
Estimated Fair Value	$ 107,662

Fair Value Measurements (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial assets:
Total assets measured at fair value on a recurring basis	$ 482,916	$ 245,867
Financial liabilities:
Total financial liabilities measured at fair value on a recurring basis	47,702
Stock price appreciation milestones
Financial liabilities:
Stock price appreciation milestones	47,702
Money market funds
Financial assets:
Money market funds	167,347	84,814
U.S. Treasury debt securities
Financial assets:
Investments	39,767	60,303
Non-U.S. government securities
Financial assets:
Investments	5,056
Corporate debt securities
Financial assets:
Investments	160,003	100,750
Municipal securities
Financial assets:
Investments	3,081
Commercial Paper
Financial assets:
Investments	107,662
Quoted prices in Active Market for Identical Assets (Level 1)
Financial assets:
Total assets measured at fair value on a recurring basis	207,114	145,117
Quoted prices in Active Market for Identical Assets (Level 1) \| Money market funds
Financial assets:
Money market funds	167,347	84,814
Quoted prices in Active Market for Identical Assets (Level 1) \| U.S. Treasury debt securities
Financial assets:
Investments	39,767	60,303
Significant Other Observable Inputs (Level 2)
Financial assets:
Total assets measured at fair value on a recurring basis	275,802	100,750
Significant Other Observable Inputs (Level 2) \| Non-U.S. government securities
Financial assets:
Investments	5,056
Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Financial assets:
Investments	160,003	$ 100,750
Significant Other Observable Inputs (Level 2) \| Municipal securities
Financial assets:
Investments	3,081
Significant Other Observable Inputs (Level 2) \| Commercial Paper
Financial assets:
Investments	107,662
Significant Unobservable Inputs (Level 3)
Financial liabilities:
Total financial liabilities measured at fair value on a recurring basis	47,702
Significant Unobservable Inputs (Level 3) \| Stock price appreciation milestones
Financial liabilities:
Stock price appreciation milestones	$ 47,702

Fair Value Measurements (Details 3) $ in Thousands	12 Months Ended
Fair Value Measurements (Details 3) $ in Thousands	Dec. 31, 2020 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value of stock price appreciation milestones	$ 47,702
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at the beginning of the period	0
Change in fair value of stock price appreciation milestones	47,702
Balance at the end of the period	$ 47,702

Accrued Expenses and Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current accrued expenses
Accrued payroll and other employee benefits	$ 4,815	$ 5,329
Accrued clinical trial related costs	5,244	5,976
Accrued other	5,505	3,392
Total current accrued expenses	$ 15,564	$ 14,697

Accrued Expenses and Long-Term Debt (2017 Term Loan) (Details 2) - USD ($) $ in Millions		12 Months Ended
	Nov. 13, 2019	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Aggregate interest expense		$ 1.8	$ 1.7
Loan and Security Agreement
Debt Instrument [Line Items]
Repayments of debt amount	$ 14.2
Principal amount of the final fee payment	13.0
Final payment fee	$ 1.2

Leases (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Leases (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee Lease Description [Line Items]
Lessee, operating lease, option to extend		These leases have terms varying from one to approximately sixteen years, with renewal options of up to ten years
Lessee, operating lease, existence of option to extend		true
Letters of credit outstanding amount		$ 15,200	$ 200	$ 200
Future minimum payments under the operating leases		$ 194,026
Remaining weighted-average lease term		13 years 3 months 18 days
Operating lease liabilities, weighted-average discount rate		8.40%
Total short-term lease expense		$ 1,200	$ 1,100
Aggregate contractual rent expense				$ 2,300
The Premises 2020 Lease Agreement
Lessee Lease Description [Line Items]
Lessee, operating lease, option to extend	The Company has the option to extend the lease for two successive five-year periods. The Company also has a one-time option to terminate the lease after 10 years from the Rent Commencement Date
Lessee, operating lease, existence of option to extend	true
Lease term	15 years
Option to terminate lease	10 years
Tenant improvements		$ 18,200
Early termination fees	$ 30,000
Letters of credit outstanding amount	15,000
Minimum
Lessee Lease Description [Line Items]
Lease term		1 year
Future minimum payments under the operating leases		$ 194,000
Maximum
Lessee Lease Description [Line Items]
Lease term		16 years
Maximum \| The Premises 2020 Lease Agreement
Lessee Lease Description [Line Items]
Renewal term		10 years
Aggregate tenant improvements of the premises	$ 29,800

Leases (Details 1) - USD ($) $ in Thousands	12 Months Ended
Leases (Details 1) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Lease Cost [Abstract]
Straight-line lease expense	$ 12,076	$ 3,781
Variable lease expense	2,245	2,330
Total operating lease expense	$ 14,321	$ 6,111

Leases (Details 2) $ in Thousands	Dec. 31, 2020 USD ($)
Operating Lease Liabilities Payments Due [Abstract]
2021	$ 10,824
2022	12,610
2023	12,988
2024	13,378
2025	13,779
Thereafter	130,447
Total undiscounted lease payments	194,026
Less: imputed interest	(85,247)
Less: amounts associated with tenant improvement allowance not yet utilized	(11,481)
Total lease liability	$ 97,298

Convertible Preferred Stock and Stockholders' Equity (Details 3) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Restricted Stock Units
Balance at the beginning of the period	520,000
Granted	1,033,323
Vested	(85,000)
Cancelled	(66,591)
Balance at the end of the period	1,401,732	520,000
Expected to vest at the end of the period	1,401,732
Weighted-Average Grant Date Fair Value per Share
Balance at the beginning of the period	$ 16.41
Granted	22.86
Vested	16.34
Cancelled	21.94
Balance at the end of the period	20.91	$ 16.41
Expected to vest at the end of the period	$ 20.91
Weighted Average Remaining Vesting Period
Outstanding at the end of the period	2 years 7 months 20 days	2 years 7 months 20 days
Expected to vest at the end of the period	2 years 7 months 20 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 127,459	$ 10,176
Restricted stock units expected to vest at December 31, 2020	$ 127,459

Convertible Preferred Stock and Stockholders' Equity (Details 6) - shares	Dec. 31, 2020	Dec. 31, 2019	May 10, 2016	Sep. 13, 2013
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	29,704,815	27,708,900
Convertible Preferred Stock (if converted)
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	13,972,745	13,972,745
Inducement Plan
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	550,000	279,178	500,000
Employee Stock Option
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	10,432,822	9,327,742
Stock Compensation Plan
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	2,618,516	2,880,235
Restricted Stock Units (RSUs)
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	1,401,732	520,000
Employee Stock
Weighted-average assumptions to determine fair value of stock options
Shares reserved for issuance	729,000	729,000		729,000

Income Taxes (Details 2) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details 2) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 144,066	$ 94,569
U.S. Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	186,400
Operating loss carryforwards indefinite life	$ 67,000
Percent of taxable income offset	48.00%
Net operating loss carryforward expiration year	2027
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 188,000
Net operating loss carryforward expiration year	2028

Income Taxes (Details 3) $ in Millions	12 Months Ended
Income Taxes (Details 3) $ in Millions	Dec. 31, 2020 USD ($)
Tax Credit Carryforward [Line Items]
Cumulative changes in ownership percentage	50.00%
Period of change in ownership	3 years
Californian
Tax Credit Carryforward [Line Items]
Income tax examination, year under examination	2016
U.S. Federal
Tax Credit Carryforward [Line Items]
Income tax examination, year under examination	2017
U.S. Federal \| Research and development
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 18.0
Tax credit carryforward expiration year	2035
California \| Research and development
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 12.9

Income Taxes (Details 4) - USD ($)	12 Months Ended
Income Taxes (Details 4) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in the Company's unrecognized tax benefits
Beginning unrecognized tax benefits	$ 16,822,000	$ 13,547,000	$ 11,800,000
Increase related to current year tax positions	1,837,000	3,196,000	1,798,000
Increase related to prior year tax positions	1,120,000	79,000	148,000
Decrease related to prior year tax positions			(199,000)
Ending unrecognized tax benefits	19,779,000	$ 16,822,000	$ 13,547,000
Income Taxes
Unrecognized tax benefit	0
Unrecognized tax benefits that, if recognized, would reduce the effective tax rate	$ 0

Employee Benefits (Details) - USD ($)		12 Months Ended
Employee Benefits (Details) - USD ($)	Jan. 02, 2009	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Minimum age of employees	21 years
Matching contributions under 401(k) plan		$ 0

Commitments and Contingencies (Details) $ in Millions	12 Months Ended
Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2020 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Minimum annual payments to maintain licenses	$ 0.4

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Aggregate purchase price of common stock		$ 188,784	$ 162,406	$ 134,791
Subsequent Event \| Pre-Funded Warrants
Debt Instrument [Line Items]
Number of shares to be purchased	257,310
Exercise price of warrants	$ 85.499
Terms of exercise	The Pre-Funded Warrants are exercisable at any time after the date of issuance. A holder of Pre-Funded Warrants may not exercise the Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 9.99% of the number of shares of the Company’s common stock outstanding immediately after giving effect to such exercise. A holder of Pre-Funded Warrants may increase or decrease this percentage not in excess of 19.99% by providing at least 61 days’ prior notice to the Company.
Maximum percentage of common stock ownership together with affiliates required for exercise after pre funded warrants exercise	9.99%
Maximum percentage of common stock ownership after change upon notice.	19.99%
Warrant, exercise price, decrease	$ 0.001
Subsequent Event \| January 2021 Public Offering
Debt Instrument [Line Items]
Aggregate purchase price of common stock	$ 460,000
Net proceeds from issuance of shares after related underwriting discounts and commissions and estimated expenses	$ 432,100
Issuance of common stock in conjunction with public offering (in shares)	5,100,000
Share issue price (in dollars per share)	$ 85.50