Global Blood Therapeutics (GBT) 10-K 24 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 18, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	Global Blood Therapeutics, Inc.
Entity Filer Category	Large Accelerated Filer
Trading Symbol	GBT
Entity Emerging Growth Company	false
Entity Small Business	false
Document Transition Report	false
Entity Common Stock, Shares Outstanding		62,156,860
Document Annual Report	true
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity File Number	001-37539
Entity Tax Identification Number	27-4825712
Entity Shell Company	false
Entity Address, Address Line One	181 Oyster Point Boulevard
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
City Area Code	650
Local Phone Number	741-7700
Entity Address, Postal Zip Code	94080
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001629137
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 1,606.1
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	true

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 494,766	$ 302,237
Short-term marketable securities	66,126	307,732
Accounts receivable, net	17,500	2,637
Inventories	40,223	1,277
Prepaid expenses	12,599	9,422
Other assets, current	949	4,692
Total current assets	632,163	627,997
Property and equipment, net	37,882	27,113
Long-term marketable securities		85,030
Operating lease right-of-use assets	50,722	52,775
Restricted cash	2,436	2,395
Other assets, noncurrent	799	789
Total assets	724,002	796,099
Current liabilities:
Accounts payable	19,078	10,621
Accrued liabilities	31,133	41,358
Accrued compensation	23,985	17,578
Other liabilities, current	4,836	1,896
Total current liabilities	79,032	71,453
Long-term debt	148,815	73,559
Operating lease liabilities, noncurrent	79,176	72,359
Other liabilities, noncurrent	822	34
Total liabilities	307,845	217,405
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized at December 31, 2020 and 2019, respectively, and none issued and outstanding as of December 31, 2020 and 2019
Common stock, $0.001 par value, 150,000,000 shares authorized at December 31, 2020 and 2019, respectively; 61,898,090 and 60,644,380 shares issued and outstanding at December 31, 2020 and 2019, respectively	62	61
Additional paid-in capital	1,402,262	1,316,795
Accumulated other comprehensive income	302	754
Accumulated deficit	(986,469)	(738,916)
Total stockholders' equity	416,157	578,694
Total liabilities and stockholders' equity	$ 724,002	$ 796,099

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	61,898,090	60,644,380
Common stock, shares outstanding	61,898,090	60,644,380

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues [Abstract]
Product sales, net	$ 123,803	$ 2,108
Costs and operating expenses:
Cost of sales	1,986	48
Research and development	155,122	174,556	$ 131,307
Selling, general and administrative	210,851	117,088	51,435
Gain on lease modification	(984)	(8,301)
Total costs and operating expenses	366,975	283,391	182,742
Loss from operations	(243,172)	(281,283)	(182,742)
Other income (expense):
Interest income	5,834	15,591	8,964
Interest expense	(9,809)	(894)	(346)
Other expenses, net	(406)	(180)	(69)
Total other income (expense), net	(4,381)	14,517	8,549
Net loss	(247,553)	(266,766)	(174,193)
Other comprehensive loss:
Net unrealized gain (loss) on marketable securities, net of tax	(452)	802	288
Comprehensive loss	$ (248,005)	$ (265,964)	$ (173,905)
Basic and diluted net loss per common share	$ (4.04)	$ (4.57)	$ (3.41)
Weighted-average number of shares used in computing basic and diluted net loss per common share	61,334,037	58,321,612	51,150,728

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2017	$ 318,804	$ 46	$ 617,051	$ (336)	$ (297,957)
Beginning Balance, Shares at Dec. 31, 2017		46,131,723
Issuance of common stock upon equity offerings, net of issuance costs	396,034	$ 8	396,026
Issuance of common stock upon equity offerings, net of issuance costs, Shares		8,403,826
Issuance of common stock upon exercise of stock options	6,022	$ 1	6,021
Issuance of common stock upon exercise of stock options, Shares		596,434
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(6,252)	$ 1	(6,253)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		255,039
Issuance of common stock pursuant to ESPP purchases	1,647		1,647
Issuance of common stock pursuant to ESPP purchases, Shares		61,031
Vesting of restricted stock purchases	369		369
Vesting of restricted stock purchases, Shares		192,246
Stock-based compensation expense	30,080		30,080
Net unrealized gain (loss) on marketable securities	288			288
Net loss	(174,193)				(174,193)
Ending Balance at Dec. 31, 2018	572,799	$ 56	1,044,941	(48)	(472,150)
Ending Balance, Shares at Dec. 31, 2018		55,640,299
Issuance of common stock upon equity offerings, net of issuance costs	219,671	$ 4	219,667
Issuance of common stock upon equity offerings, net of issuance costs, Shares		3,986,890
Issuance of common stock upon exercise of stock options	11,636	$ 1	11,635
Issuance of common stock upon exercise of stock options, Shares		538,503
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	(7,617)		(7,617)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		368,357
Issuance of common stock pursuant to ESPP purchases	2,361		2,361
Issuance of common stock pursuant to ESPP purchases, Shares		63,280
Vesting of restricted stock purchases	157		157
Vesting of restricted stock purchases, Shares		47,051
Stock-based compensation expense	45,651		45,651
Net unrealized gain (loss) on marketable securities	802			802
Net loss	(266,766)				(266,766)
Ending Balance at Dec. 31, 2019	578,694	$ 61	1,316,795	754	(738,916)
Ending Balance, Shares at Dec. 31, 2019		60,644,380
Issuance of common stock upon exercise of stock options	$ 13,328		13,328
Issuance of common stock upon exercise of stock options, Shares	525,788	525,788
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes	$ (5,287)	$ 1	(5,288)
Issuance of common stock upon vesting of restricted share units, net of shares withheld for employee taxes, Shares		629,857
Issuance of common stock pursuant to ESPP purchases	4,137		4,137
Issuance of common stock pursuant to ESPP purchases, Shares		98,065
Stock-based compensation expense	73,290		73,290
Net unrealized gain (loss) on marketable securities	(452)			(452)
Net loss	(247,553)				(247,553)
Ending Balance at Dec. 31, 2020	$ 416,157	$ 62	$ 1,402,262	$ 302	$ (986,469)
Ending Balance, Shares at Dec. 31, 2020		61,898,090

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (247,553)	$ (266,766)	$ (174,193)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	8,323	8,605	4,607
Amortization (accretion) of premium (discount) on marketable securities	119	(2,057)	(661)
Non-cash interest expense	1,523	43
Amortization of operating lease right-of-use assets	2,500	1,327
Stock-based compensation	71,477	45,651	30,080
Gain on lease modification	(984)	(8,301)
Loss from disposal of fixed assets, net			45
Changes in operating assets and liabilities:
Accounts receivables	(14,863)	(2,637)
Inventories	(36,779)	(1,277)
Prepaid expenses	(702)	(3,085)	(2,500)
Other assets, current	(23)	(2,112)	(1,278)
Accounts payable	8,374	4,499	(1,285)
Accrued liabilities	(10,089)	24,706	8,031
Accrued compensation	6,407	7,543	1,457
Other liabilities, current	(587)	(1,482)	742
Operating lease liabilities	173	893
Other liabilities, noncurrent	822	33	(420)
Net cash used in operating activities	(211,862)	(194,417)	(135,375)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(8,754)	(3,460)	(4,824)
Proceeds from sale of property and equipment		45	75
Purchases of marketable securities	(57,936)	(434,919)	(361,405)
Maturities of marketable securities	384,002	361,473	181,997
Net cash provided by (used in) investing activities	317,312	(76,861)	(184,157)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs		219,443	396,501
Proceeds from issuance of long-term debt, net of debt issuance costs	74,799	72,475
Proceeds from issuance of common stock in settlement of employee stock purchase plan and exercise of stock options	17,608	13,857	7,657
Taxes paid related to net share settlement of equity awards	(5,287)	(7,617)	(6,252)
Net cash provided by financing activities	87,120	298,158	397,906
Net increase in cash, cash equivalents and restricted cash	192,570	26,880	78,374
Cash, cash equivalents and restricted cash at beginning of period	304,632	277,752	199,378
Cash, cash equivalents and restricted cash at end of period	497,202	304,632	277,752
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest	6,283
SUPPLEMENTAL DISCLOSURES OF NON-CASH FINANCING INFORMATION:
Accrued issuance costs	(59)	85	467
Leasehold improvements paid for by landlord	10,709	17,231
Accrued purchase of property and equipment	6	78	48
RECONCILIATION OF CASH, CASH EQUIVALENTS, AND RESTRICTED CASH TO THE CONDENSED CONSOLIDATED BALANCE SHEETS
Cash, cash equivalents	494,766	302,237	275,357
Restricted cash	2,436	2,395	2,395
Total cash and cash equivalents and restricted cash	$ 497,202	$ 304,632	$ 277,752

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Global Blood Therapeutics, Inc., or the Company, we, us, or our, was incorporated in Delaware in February 2011 and commenced operations in May 2012. We are a biopharmaceutical company dedicated to the discovery, development and delivery of life-changing treatments that provide hope to underserved patient communities. In late November 2019, we received U.S. Food and Drug Administration, or FDA, accelerated approval for our first medicine, Oxbryta ® Need for Additional Capital In the course of our development activities, we have sustained operating losses and we expect such losses to continue over the next several years. Our ultimate success depends on the outcome of our commercialization of Oxbryta and research and development activities. Since inception through December 31, 2020, we have incurred cumulative net losses of $986.5 million. We expect to incur additional losses for the foreseeable future to commercialize Oxbryta and conduct product research and development, and expect to potentially raise additional capital to fully implement our business plan. If needed, we intend to raise such capital through borrowings, the issuance of additional equity, and potentially through strategic alliances with partner companies or other transactions. However, if such financing is not available at adequate levels, we will need to re-evaluate

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP. Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of variable consideration and costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated upon consolidation. Segment Reporting We have determined that we operate in a single segment based upon the way the business is organized for making operating decisions and assessing performance. We have only one operating segment related to the development of pharmaceutical products. All property and equipment is maintained in the United States. Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist primarily of amounts invested in money market accounts, are stated at fair value. Investments in Marketable Securities We invest in marketable securities, primarily money market funds, corporate debt securities, government securities, government agency securities, and certificates of deposits. We classify our marketable securities as available-for-sale available-for-sale available-for-sale We regularly review all of our investments for other-than-temporary declines in estimated fair value. Our review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. When we determine that the decline in estimated fair value of an investment is below the amortized cost basis and the decline is other than temporary, we reduce the carrying value of the security and record a loss for the amount of such decline. Fair Value Measurement The carrying amounts of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Concentration of Risk Credit Risk We invest in a variety of financial instruments and, by our Board approved investment policy, limit the amount of credit exposure with any one issuer, industry or geographic area for investments other than instruments backed by the U.S. federal government. Major Customers We have entered into distribution agreements with certain limited specialty pharmacies and a specialty distributor. For the year ended December 31, 2020, our two largest customers represented approximately 92% of our product revenue and approximately 88% of our accounts receivable balance at December 31, 2020. Major Suppliers We do not currently have any of our own manufacturing facilities, and therefore depend on an outsourced manufacturing strategy for the production of Oxbryta for commercial use and for the production of our product candidates for clinical trials. We have contracts in place with one third-party manufacturer that is approved for the commercial production of Oxbryta and two third-party suppliers that are approved for Oxbryta’s active pharmaceutical ingredient. Although there are potential sources of supply other than our existing manufacturers and suppliers, any new supplier would be required to qualify under applicable regulatory requirements. Accounts Receivables, net Accounts receivables are recorded net of estimates of variable consideration for which reserves are established and which result from discounts and chargebacks that are offered within contracts between us and a limited number of specialty pharmacies and a specialty distributor in the United States. These reserves are classified as reductions of accounts receivable. We estimate the allowance for doubtful accounts using current expected credit loss model, or CECL model. Under the CECL model, the allowance for doubtful accounts reflects the net amount expected to be collected from the account receivables. We evaluate the collectability of these cash flow based on the asset’s amortized cost, the risk of loss even when that risk is remote, losses over an asset’s contractual life, and other relevant information available to us. Accounts receivable balances are written off against the allowance when it is probable that the receivable will not be collected. Given the nature and history of our accounts receivable, we determined that an allowance for doubtful accounts was not required at December 31, 2020. Inventories Inventories are stated at the lower of cost or estimated net realizable value, on a first-in, work-in-process, We began capitalizing costs as inventory when the product candidate received regulatory approval. Prior to regulatory approval, we recorded inventory costs related to product candidates as research and development expenses. We periodically assess the recoverability of our inventory and reduce the carrying value of the inventory when items are determined to be obsolete, defective or in excess of forecasted sales requirements. Inventory write-downs for excess, defective and obsolete inventory are recorded as a cost of sales. There have been no write-downs of our inventories for the periods presented. Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which is three years for computer equipment and five years for laboratory equipment. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begins at the time the asset is placed in service. Maintenance and repairs are charged as expense in the statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations. Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. There have been no impairments of our long-lived assets for the periods presented. Restricted Cash Restricted cash consists of cash deposits held by our financial institution as collateral for our letter of credit under our facility lease. Accruals of Research and Development and Manufacturing Costs We record accruals for estimated costs of research, nonclinical and clinical studies and manufacturing development. These costs are a significant component of our research and development expenses. A substantial portion of our ongoing research and development activities are conducted by third-party service providers, including contract research organizations and contract manufacturing organizations. We also accrue for estimated costs of manufacturing activities for inventories. These costs are a significant component of the cost of our inventory. We accrue the costs incurred under our agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. We determine the accruals for research and development costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the clinical studies and the agreed-upon fee to be paid for such services. The accrual for contract manufacturing activities is based on an estimate of manufacturing activities completed to date, contractual rates, and amounts invoiced and paid to date at the end of each reporting period. We determine the percentage of manufacturing activities completed to date based on discussions with the contract manufacturing organizations , oversight of the manufacturing activities and anticipated timeline. As actual costs become known, we adjust our accruals. We have not experienced any material deviations between accrued costs and actual costs. However, actual clinical and manufacturing services performed, number of subjects enrolled, and the rate of subject enrollment may vary from our estimates, resulting in adjustments to research and development costs or inventories in future periods. Changes in these estimates that result in material changes to our accruals of research and development and manufacturing costs could materially affect our results of operations or amounts of inventories capitalized. Revenue Recognition Pursuant to Accounting Standards Codification, Topic 606, Revenue from Contracts with Customers , To determine revenue recognition for arrangements that we determine are within the scope of ASC 606, we perform the following five steps: (i) identify the contract(s) 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 in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation. We only apply the five-step model to contracts when it is probable that we will collect substantially all of the consideration we are entitled to in exchange for the goods or services we transfer to the customer. Product sales, net Our product sales consist of U.S. sales of Oxbryta, which we began shipping to customers in December 2019. Prior to December 2019, we had no product sales. We sell Oxbryta to a limited number of specialty pharmacies and a specialty distributor, or collectively, Customers. These agreements with our Customers provide for transfer of title to the product at the time the product has been delivered to the Customers. The Customers subsequently dispense our products directly to a patient or resell our products to hospitals and certain pharmacies. We recognize revenue on product sales when the Customers obtain control of our product, which occurs at a point in time, typically upon delivery to our Customers. It is at that point that we have a right to payment and that our Customers obtain title and the risks and rewards of ownership. Shipping and handling activities are considered to be fulfillment activities rather than a separate performance obligation. Payment terms are typically 30-60 We consider the effects of items that can decrease the transaction price, such as variable consideration and consideration payable to Customers or payer. Amounts related to such items are estimated at contract inception and updated at the end of each reporting period as additional information becomes available. The amount of variable consideration may be constrained and is included in the transaction price only to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Revenue from product sales is recorded after considering the impact of the following variable consideration amounts along with the constraint at the time of revenue recognition: Rebates: Prompt payment discounts Co-payment co-payment co-payment co-payment co-payment Medicare Part D Coverage Gap: Product returns: Chargebacks chargebacks in the same period that the related revenue is recognized, resulting in a reduction of product revenue and receivables. Distributor fees: Other revenue recognition considerations Oxbryta is our only product. The only performance obligation included in our contracts is the delivery of Oxbryta to our Customers. Therefore, no allocation of transaction price amongst performance obligations is necessary. Consequently, the transaction price determined after considering the impacts of variable consideration is recognized at the time control is transferred to our Customers, which is upon delivery of Oxbryta to our Customers. Because all sales of Oxbryta are in the United States and because our Customers are each a large distributor with similar variable consideration impacts, we provide revenue numbers on a total basis without further disaggregation. Additionally, we do not have any contract assets or liabilities, other than accounts receivable, related to our sales of Oxbryta. Cost of Sales Cost of sales consists primarily of direct and indirect costs related to the manufacturing of Oxbryta products sold, including third-party manufacturing costs, packaging services, freight, storage costs, allocation of overhead costs of employees involved with production, and Oxbryta net sales-based royalties payable to the Regents of the University of California. Costs incurred prior to FDA approval of Oxbryta in November 2019 have been recorded as research and development expense in our consolidated statement of operations and comprehensive loss. Leases Pursuant to Accounting Standards Codification, Topic 842, Leases adopted on January 1, 2019 , Right-of-use, As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the commencement date in determining the present value of future payments. We consider our credit risk, term of the lease, and total lease payments and adjust for the impact of collateral, as necessary, when calculating our incremental borrowing rates. The lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. Lease cost for our operating leases is recognized on a straight-line basis over the lease term. We have elected to not separate lease and non-lease non-lease ROU assets and operating lease liabilities are remeasured upon certain modifications to leases using the present value of remaining lease payments and estimated incremental borrowing rate upon lease modification. Leases (Topic 840) Prior to the Adoption of Topic 842 We enter into lease agreements for our office and laboratory facilities. These leases are classified as operating leases. Rent expense is recognized on a straight-line basis over the noncancelable term of the lease and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability, which is included within other liabilities on the consolidated balance sheet. Incentives granted under our facilities leases, including rent holiday and allowances to fund leasehold improvements, are deferred and are recognized as adjustments to rental expense on a straight-line basis over the noncancelable term of the lease. Comprehensive Income (Loss) Comprehensive income (loss) is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner Research and Development Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on our behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed. Long-term Debt Long-term debt consists of our loan agreement, or Term Loan, with funds managed by Pharmakon Advisors LP, which are BioPharma Credit PLC, as collateral agent and a lender, and Biopharma Credit Investments V (Master) LP, as a lender, and collectively, the Lenders. We accounted for the Term Loan as a debt financing arrangement. Interest expense is accrued using the effective interest rate method over the estimated period the debt will be repaid. Debt issuance costs have been recorded as a debt discount in our consolidated balance sheets and are being amortized and recorded as interest expense throughout the life of the Term Loan using the effective interest rate method. We consider whether there are any embedded features in our debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging There are no embedded features identified from our Term Loan that require bifurcation and separating accounting. Stock-Based Compensation We measure and recognize stock-based compensation expense, including employee and non-employee Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. We recognize benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. It is our policy to include penalties and interest expense related to income taxes as a component of other expense and interest expense, respectively, as necessary. To date, there have been no interest or penalties incurred in relation to the unrecognized tax benefits. Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given our net loss. Recent Accounting Pronouncements In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes 2019-12 Accounting Pronouncements Adopted In August 2018, FASB, issued ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use 350-40), Arrangement That Is a Service Contract 2018-15. No. 2018-15 internal-use 350-40 No. 2018-15 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) No. 2018-13 No. 2018-13 In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (Topic 326) U.S. GAAP an impairment model that is based on expected losses rather than incurred losses, which is known as the current expected credit loss, or CECL model. The CECL model applies to most debt instruments (other than those measured at fair value), trade and other receivables, financial guarantee contracts, and loan commitments. Available-for-sale available-for-sale No. 2016-13

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). Our financial instruments consist of cash and cash equivalents, marketable securities, accounts receivables, accounts payable and accrued liabilities. Cash and cash equivalents and marketable securities reported at their respective fair values on our consolidated balance sheets. The remaining financial instruments are reported on our c b s Assets and liabilities recorded at fair value on a recurring basis in the consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1— Level 2— Level 3— The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands): December 31, 2020 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 486,174 $ 486,174 $ — $ — Corporate debt securities 29,804 — 29,804 — U.S. government agency securities 15,943 — 15,943 — Certificates of deposits 243 — 243 — U.S. government securities 20,136 — 20,136 — Total financial assets $ 552,300 $ 486,174 $ 66,126 $ — December 31, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 250,535 $ 250,535 $ — $ — Corporate debt securities 152,149 — 152,149 — U.S. government agency securities 95,032 — 95,032 — Certificates of deposits 6,282 — 6,282 — U.S. government securities 140,244 — 140,244 — Total financial assets $ 644,242 $ 250,535 $ 393,707 $ — We estimate the fair values of our investments in corporate debt securities, government and government related securities and certificates of deposits by taking into consideration valuations obtained from third-party pricing services. The fair value of our marketable securities classified within Level 2 is based upon observable inputs that may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided A-1/P-1/F1

Available-for-Sale Securities

Available-for-Sale Securities	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale Securities	4. Available-for-Sale Estimated fair values of available-for-sale available-for-sale December 31, 2020 December 31, 2019 Amortized Unrealized Unrealized Estimated Amortized Unrealized Unrealized Estimated Financial Assets: Money market funds $ 486,174 $ — $ — $ 486,174 $ 250,535 $ — $ — $ 250,535 Corporate debt securities 29,641 163 — 29,804 151,773 384 (8 ) 152,149 U.S. government agency securities 15,906 37 — 15,943 94,963 73 (4 ) 95,032 Certificates of deposits 241 2 — 243 6,239 43 — 6,282 U.S. government securities 20,036 100 — 20,136 139,978 266 — 140,244 Total $ 551,998 $ 302 $ — $ 552,300 $ 643,488 $ 766 $ (12 ) $ 644,242 The following table summarizes the classification of the available-for-sale c b s December 31, December 31, Cash and cash equivalents $ 486,174 $ 251,480 Short-term marketable securities 66,126 307,732 Long-term marketable securities — 85,030 Total $ 552,300 $ 644,242

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	5. Balance Sheet Components Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2020 2019 Laboratory equipment $ 11,922 $ 8,314 Computer equipment 3,023 2,224 Leasehold improvements 32,281 13,785 Construction-in-progress 517 19,289 Total property and equipment 47,743 43,612 Less: accumulated depreciation and amortization (9,861 ) (16,499 ) Property and equipment, net $ 37,882 $ 27,113 Depreciation expense was $8.3 million for the year ended December 31, 2020, $8.6 million for the year ended December 31, 2019 and $4.7 million for the year ended December 31, 2018. Refer to Note 8—Commitments and Contingencies for details on acceleration of depreciation expenses recognized during the years ended December 31, 2020 and 2019. Accrued Liabilities Accrued liabilities consist of the following (in thousands): December 31, 2020 2019 Accrued research and development costs $ 10,677 $ 26,480 Accrued manufacturing costs 9,125 9,466 Accrued professional and consulting services 4,107 4,564 Accrued sales deductions 6,405 529 Other 819 319 Total accrued liabilities $ 31,133 $ 41,358 Other liabilities, current Other liabilities consist of the following (in thousands): December 31, 2020 2019 Operating lease liabilities, current $ 4,836 $ 1,866 Other payable — 30 Total other liabilities, current $ 4,836 $ 1,896

Inventories

Inventories	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block [Abstract]
inventories	6. Inventories We began capitalizing inventories in November December 31, 2020 2019 Raw materials $ 11,273 $ 700 Work-in-process 26,994 525 Finished goods 1,956 52 Total inventories $ 40,223 $ 1,277

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block [Abstract]
Long-term Debt	7. Long-term Debt Term Loan On December 17, 2019, we entered into the Loan Agreement, or Term Loan, with funds managed by Pharmakon Advisors LP, which are BioPharma Credit PLC, as collateral agent, Biopharma Credit Investments V (Master) LP, as a lender, and BPCR Limited Partnership, as a lender, and collectively, the Lenders, for a senior secured credit facility consisting of an initial tranche of $75.0 million and the option to draw an additional $75.0 million until December 31, 2020. The first tranche, in the amount of $75.0 million, was funded in connection with the closing date of the Term Loan in December 2019, and the second tranche of the Term Loan, in the amount of $75.0 million was funded in November 2020. The Term Loan carries a 72-month 3-month We have the option to prepay all or a portion of the borrowed amounts under the Term Loan. If we exercise this option, we must pay a prepayment fee between 1% and 3% of the principal amount being prepaid depending on the timing of the prepayment, or Prepayment Fee. If the prepayment occurs before December 2022, we must also pay an amount equal to the sum of all interest that would have accrued and been payable from date of prepayment through December 2022, or Make Whole Amount. We are obligated to pay an additional fee to the Lenders determined by multiplying the principal amount being paid or prepaid multiplied by 2%, or Paydown Fee, when such payments are made. In the event of default or change in control, all unpaid principal and all accrued and unpaid interest amounts (if any) become immediately due and payable, at which point, we will be subject to the Prepayment Fee, the Make Whole Amount (if any) and the Paydown Fee. Events of default include, but are not limited to, a payment default, a material adverse change, and insolvency. The obligations under the Term Loan are secured by a first priority security interest in and a lien on substantially all of our assets, subject to certain exceptions. Debt issuance costs paid directly to the Lenders of $1.1 million and the other debt issuance costs of $0.5 million were treated as discounts on the Term Loan. These debt discounts along with the Paydown Fee are being amortized or accreted to interest expenses throughout the life of the Term Loan using the effective interest rate method. As of December 31, 2020, there were unamortized issuance costs and debt discounts of $ million, which were recorded as a direct deduction from the Term Loan on the consolidated balance sheet. In addition, we paid the Lenders $ million for the option to draw the additional $ million, which was capitalized as a deferred asset and amortized on a straight-line basis through December 31, 2020. Any remaining unamortized amount is reclassed to debt discount at the time of closing of the second tranche of the Term Loan. We closed the second tranche of the Term Loan in November 2020 and $ million of the unamortized deferred asset related to the option to draw the second tranche was reclassed as the discount on the notes payable. Future payments of principal and interest on the Term Loan as of December 31, 2020 (in thousands): 2021 13,500 2022 13,500 2023 62,813 2024 58,313 2025 53,812 Total minimum payments 201,938 Less amount representing interest (48,938 ) Less amount representing Paydown Fee (3,000 ) Long-term debt, gross 150,000 Discount on notes payable (1,596 ) Accretion of Paydown Fee 411 Long-term debt $ 148,815

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Leases We have operating leases for our headquarters, where we have office and research and development laboratory facilities, and equipment. Our leases have remaining lease terms of 1 to 10 years. Most of these leases require monthly lease payments that may be subject to annual increases throughout the lease term. Certain of these leases include renewal options at our election, with renewal terms that can extend the lease term from 1 to 10 years. These optional periods have not been considered in the determination of the right-of-use Lease costs included in operating expense in the consolidated statement of operations and comprehensive loss in relation to these operating leases were $12.4 million and $7.8 million for the year ended December 31, 2020 and 2019, respectively. Included in these lease costs were variable lease costs, which were not included within the measurement of our operating ROU assets and operating lease liabilities in the amount of $2.6 million and $2.5 million for the year ended December 31, 2020 and 2019, respectively. The variable lease cost is comprised primarily of our cost in certain research and development arrangements that contain embedded equipment, and our proportionate share of operating expenses, property taxes, and insurance in relation with our facility lease. These costs are classified as operating lease expense due to our election to not separate lease and non-lease Supplemental information related to leases for the period reported is as follows (in thousands, except weighted-average remaining lease term and weighted-average discount rate): For the year ended 2020 2019 ROU assets obtained in exchange for new operating lease upon adoption of ASC 842 $ — $ 14,177 Adjustment to ROU assets as a result of the lease modification for the Prior Premises (106 ) (13,802 ) ROU assets obtained for new operating lease liabilities 205 53,727 Operating lease liabilities arising from obtaining ROU assets 205 25,929 Cash paid for amounts included in the measurement of lease liabilities 7,696 4,481 Weighted-average remaining lease term of operating leases (in years) 9.2 10.1 Weighted-average discount rate of operating leases 8.66 % 8.66 % The majority of our lease costs are driven by our operating lease for our headquarters in South San Francisco, where we have office and research and development laboratory facilities. In March 2017, we entered into a noncancelable operating lease, or Original Lease, for approximately 67,185 square feet of space in South San Francisco, California, or Prior Premises. In August 2018, we entered into an amendment to the Original Lease, or Lease Amendment, to relocate the leased premises from the Prior Premises to a to-be-constructed 10-year 10-year On October 1, 2019, we determined that the Lease Amendment for the Substitute Premises had commenced as we had the right to control the Substitute Premises, which was deemed to be a lease modification. We determined the Lease Amendment consisted of two separate contracts under ASC 842. One contract was related to a new ROU asset for the Substitute Premises, which was to be accounted for as a new lease, and the other was related to the modification of the lease term of the Prior Premises. With the commencement of the Lease Amendment, the lease term for the Original Lease was reduced, with the modified lease term expiring on June 1, 2020. We determined that the reduction of the lease term would be accounted for as a lease modification to the Prior Lease. On October 1, 2019, we remeasured the present value of future lease payments during the modified lease term to be $2.9 million, using an incremental borrowing rate of approximately 8.78%. We recognized the amount of remeasurement of the lease liability as an adjustment to the ROU asset, reducing the carrying amount of the ROU asset to zero, and recognized a gain on lease modification of $ million for the year ended December 31, 2019. An additional gain on lease modification of $ million was recognized for the year ended December 31, 2020 to write off the remaining lease liability related to the Original Lease when we vacated the building On October 1, 2019, or Substitute Premises Commencement Date, we measured the present value of future lease payments that included the expected utilization of tenant inducements, using an incremental borrowing rate of approximately 8.66%. We recorded a ROU asset and a lease liability for $53.7 million associated with the Substitute Premises. During the years ended December 31, 2020 and 2019, the landlord paid approximately $10.7 million and $17.2 million, respectively, out of tenant inducement allowances for construction of leasehold improvements at the Substitute Premises, which was recognized as an increase in the operating lease liability. The balances of the ROU asset were approximately $50.6 million and $52.8 million as of December 31, 2020 and 2019, respectively. The balances for the operating lease liability were approximately $83.8 million and $72.4 million as of December 31, 2020, and 2019, respectively. After relocating to the Substitute Premise, we surrendered and delivered the Prior Premises to the landlord in May 2020, upon which time we had no further obligations with respect to the Prior Premises other than with respect to the Initial Allowance, which we will repay to the landlord in the form of additional monthly rent with interest applied over the term of the Original Lease. Upon signing of the Lease Amendment, we re-evaluated As of December 31, 2020, the maturities of our operating lease liabilities under Topic 842 were as follows (in thousands): Year ending December 31, Amount 2021 11,841 2022 12,222 2023 12,584 2024 12,948 2025 13,368 Thereafter 60,507 Total lease payments 123,470 Less: Imputed interest (39,458 ) Present value of operating lease liabilities $ 84,012 Rent expense was $9.8 million for the year ended December 31, 2020, $5.2 million for the year ended December 31, 2019, and $3.6 million for the year ended December 31, 2018. The operating leases require us to share in prorated operating expenses and property taxes based upon actual amounts incurred; those amounts are not fixed for future periods and, therefore, are not included in the future commitments listed above. Indemnifications We indemnify each of our directors and officers for certain events or occurrences, subject to certain limits, while the director or the officer is or was serving at our request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as a director or an officer may be subject to any proceeding arising out of acts or omissions of such director in such capacity. The maximum amount of potential future indemnification is unlimited; however, we currently hold director and officer liability insurance. This insurance allows the transfer of risk associated with our exposure and may enable us to recover a portion of any future amounts paid. We believe that the fair value of these indemnification obligations is minimal. Accordingly, we have not recognized any liabilities relating to these obligations for any period presented. Contingencies In the ordinary course of business, we may be subject to legal claims and regulatory actions that could have a material adverse effect on our business or financial position. We assess our potential liability in such situations by analyzing potential outcomes, assuming various litigation, regulatory and settlement strategies. If we determine a loss is probable and its amount can be reasonably estimated, we accrue an amount equal to the estimated loss. No losses and no provision for a loss contingency have been recorded to date. Contingent Payments In December 2019, we entered into an agreement, the Syros Agreement, with Syros Pharmaceuticals, Inc., or Syros, to discover, develop and commercialize novel therapies for SCD and beta thalassemia. Under the agreement, Syros will use its leading gene control platform to identify therapeutic targets and discover drugs that potentially induce fetal hemoglobin, and we have an option to obtain an exclusive worldwide license to develop, manufacture and commercialize any compounds or products resulting from the agreement, subject to Syros’ option to co-promote Under the terms of the Syros Agreement, we paid Syros an upfront payment of $20.0 million in January 2020, and, if we exercise our option under the agreement, we may be obligated to pay Syros up to $315.0 million in option exercise, development, regulatory, commercialization and sales-based milestones per product candidate and product resulting from the agreement. We will also be obligated to pay Syros, subject to certain reductions, tiered mid- In August 2018, we entered into the License Agreement, or Roche Agreement, with F. Hoffmann-La Hoffmann-La know-how non-exclusive, the achievement of certain clinical development and regulatory milestones for inclacumab for any indication other than the SCD indication.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity Follow-on In June 2019, we completed a follow-on In December 2018, we completed a follow-on Common Stock Reserved for Issuance We have reserved sufficient shares of common stock for issuance upon the exercise of stock options, vesting of restricted stock units and restricted shares subject to future vesting. Common stockholders are entitled to dividends if and when declared by the board of directors, subject to the prior rights of any preferred stockholders. As of December 31, 2020, no common stock dividends had been declared by the board of directors. We have reserved shares of common stock for future issuance as follows: December 31, 2020 2019 Restricted stock units 2,625,056 1,848,772 Options issued and outstanding 3,327,330 3,573,860 Shares available for future grant under the 2015 Plan and 2017 Inducement Equity Plan 6,018,567 4,478,656 Employee stock purchase plan 254,590 252,655 Total 12,225,543 10,153,943

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation	10. Share-based Compensation Amended and Restated 2017 Inducement Equity Plan In January 2017, we adopted the 2017 Inducement Equity Plan and amended the plan in December 2019 with the Amended and Restated 2017 Inducement Plan, or the 2017 Inducement Plan . Under the 2017 Inducement Plan, shares of our common stock are reserved for the issuance of non-qualified stock options and other equity-based awards to induce highly-qualified prospective officers and employees who are not currently employed by us or our subsidiaries to become employed with our company. Awards granted under the 2017 Inducement Plan expire no later than 10 years non-statutory four years 1 th three years 1 th three years 2015 Stock Option and Incentive Plan In July 2015, we adopted the 2015 Stock Option and Incentive Plan, or 2015 Plan. Under the 2015 Plan, shares of our common stock are reserved for the issuance of stock options, restricted stock, and other equity-based awards to employees, non-employee non-statutory 4-year 1/8 th 4-year 2012 Stock Option and Grant Plan In 2012, we adopted the 2012 Stock Option and Grant Plan, or 2012 Plan, under which our Board of Directors was authorized to grant incentive stock options to employees, including officers and members of the Board of Directors who are also employees of ours, and non-statutory Stock Option Activity The following table summarizes activity under our stock option plans, including the 2017 Inducement Plan, 2015 Plan and the 2012 Plan and related information (in thousands, except share and per share amounts and term): Number Weighted- Weighted- Aggregate Outstanding—December 31, 2019 3,573,860 $ 36.24 7.55 Options granted 719,561 65.36 Options exercised (525,788 ) 25.35 Options canceled (440,303 ) 52.78 Outstanding—December 31, 2020 3,327,330 $ 42.07 7.02 $ 29,720 Vested and exercisable—December 31, 2020 2,151,326 $ 34.77 6.33 $ 28,616 The aggregate intrinsic value was calculated as the difference between the exercise price of the options and the fair value of our common stock as of December 31, 2020. The total intrinsic value of options exercised was $23.0 million for the year ended December 31, 2020, $23.5 million for the year ended December 31, 2019, and $23.4 million for the year ended December 31, 2018. The weighted-average estimated fair value of stock options granted was $40.76 for the year ended December 31, 2020, $32.30 for the year ended December 31, 2019, and $33.58 for the year ended December 31, 2018. Stock Options Granted to Employees with Service-based Vesting Valuation Assumptions The fair values of stock options granted to employees were calculated using the following assumptions: Year Ended December 31, 2020 2019 2018 Expected term (in years) 5.1-6.1 5.3-6.1 5.3-6.1 Volatility 69.6%-71.8% 69.8%-72.2% 68.7%-71.8% Risk-free interest rate 0.3%-1.8% 1.4%-2.6% 2.6%-3.0% Dividend yield — — — In determining the fair value of the options granted, we used the Black-Scholes-Merton option-pricing model and assumptions discussed below. Expected Term— Our expected term represents the period that the options granted are expected to be outstanding and is determined using the simplified method (based on the mid-point between the vesting date and the end of the contractual term). We have limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for our stock option grants. Expected Volatility Risk-Free Interest Rate Expected Dividend Restricted Stock Units In January 2017, the Compensation Committee of our Board of Directors approved the commencement of granting restricted stock units, or RSUs, to our employees. RSUs are share awards that entitle the holder to receive freely tradable shares of our common stock upon the completion of a specific period of continued service. RSUs are generally subject to forfeiture if employment terminates prior to the release of vesting restrictions. RSUs granted are valued at the market price of our common stock on the date of grant. We recognize noncash compensation expense for the fair value of RSUs on a straight-line basis over the requisite service period of these awards. The following table summarizes activity of RSUs granted to employees with service-based vesting under the 2017 Inducement Plan and 2015 Plan and related information (in thousands, except share, per share amounts and vesting period): Number Weighted- Weighted- Aggregate Non-vested 1,848,772 $ 49.19 1.54 $ 146,959 RSUs granted 1,577,047 64.28 RSUs vested (710,403 ) 50.84 RSUs forfeited (505,060 ) 56.30 Non-vested 2,210,356 $ 57.80 1.45 $ 95,731 Market-Condition Awards Granted to Employees 2017 Market-Condition RSU Awards On August 11, 2017, our Board of Directors approved awards up to an aggregate of 365,250 RSUs to certain of our senior management team under the 2015 Plan, the vesting of which was contingent upon a combination of continued employment and achieving certain market capitalization milestones, which we refer to as the 2017 Market-Condition RSU Awards. The 2017 Market-Condition RSU Awards would not vest until the achievement of their respective market capitalization milestones, which were required to occur on or before December 31, 2019. The grant date fair value of the 2017 Market-Condition RSU Awards was estimated using a Monte Carlo simulation model. The derived service periods, which are the estimated periods of time that would be required to satisfy the market conditions, are also determined at the grant date. We record expense on a straight-line basis over the applicable derived service periods. In 2019, 156,000 shares and 3,250 shares of 2017 Market-Condition RSU Awards were vested and were forfeited, respectively. There were no non-vested We recognized $36,500 and $3.1 million in stock-based compensation expense related to the 2017 Market-Condition RSU Awards for the year ended December 31, 2019 and December 31, 2018, respectively. No expenses recorded related to the 2017 Market-Condition RSU Awards for the year ended December 31, 2020. 2020 Market-Condition RSU Award s The Compensation Committee of our Board of Directors granted, effective June 1, 2020, awards of up to an aggregate of 414,700 RSUs to certain of our senior management, including our executive officers, under the 2015 Plan, the vesting of which is contingent upon the achievement of three escalating stock price targets, which we refer to as the 2020 Market-Condition RSU Awards. Upon the achievement of the respective stock price targets, 50% of the RSUs allotted to that tranche will vest, while the remaining 50% will vest on the first anniversary of the date the stock price target was achieved, subject to the employee’s continued employment or other service relationship with us through such vesting date. Under the terms of the awards, if the stock price targets are not achieved for all or some of the tranches on or before June 30, 2024, the unvested awards will be automatically terminated and forfeited. The compensation cost for the RSUs with a market condition is not reversed when the market condition is not satisfied. Stock Price Targets Number of Units Allotted $109.20 82,940 $145.60 145,145 $182.00 186,615 The following table summarizes activity of the 2020 Market-Condition RSU Awards under the 2015 Plan and related information (in thousands, except share, per share amounts and vesting period): Number Weighted- Weighted- Aggregate Non-vested — $ — — Granted 421,000 49.95 Vested — — Forfeited (6,300 ) 49.95 Non-vested 414,700 $ 49.95 1.21 $ 17,961 The following table summarizes the assumptions used to estimate the fair value of the market-condition awards as of the grant date: Valuation date stock price $ 68.67 Volatility 68.1 % Risk-free interest rate 0.26 % Dividend yield — At December 31, 2020, total unrecognized compensation expense related to non-vested Employee Stock Purchase Plan In July 2015, we adopted the 2015 Employee Stock Purchase Plan, or 2015 ESPP. Under the 2015 ESPP, our employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2015 ESPP provided for offering periods of six months in duration. As approved by the Compensation Committee of the Board of Directors in December 2017, the 2015 ESPP provides for offering periods of two years in duration with purchase periods occurring every six months during an offering period. The purchase periods end on either January 31 or July 31. Contributions under the 2015 ESPP are limited to a maximum of 15% of an employee’s eligible compensation. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. The 2015 ESPP was amended and restated in March 2020. The amended 2015 ESPP moves the timing of the purchase periods end on either February 28 (or February 29, if applicable) or August 31. Once each of the existing offering period ends, the next offering period immediately following will be a one-time 7-month 6-mon th one-time six-month The fair values of the rights granted under the 2015 ESPP were calculated using the following assumptions: Year Ended Year Ended Expected term (in years) 0.5 – 2.1 0.5 – 2.0 Volatility 47.0-77.0 % 46.5-75.4 % Risk-free interest rate 0.1-1.5 % 1.7-2.6 % Dividend yield — % — % Stock-Based Compensation Expense Total stock-based compensation recognized by functions was as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 18,061 $ 19,140 $ 12,747 Selling, general and administrative 53,416 26,511 17,333 Total stock-based compensation expense $ 71,477 $ 45,651 $ 30,080 Unrecognized Stock-Based Compensation Expense and Weighted-Average Remaining Amortization Period As of December 31, 2020, the unrecognized stock-based compensation cost, and the estimated weighted-average amortization period, using the straight-line attribution method, was as follows (in thousands, except amortization period): Unrecognized Compensation Weighted- remaining amortization Stock $ 38,440 2.3 Restricted stock units 110,837 2.7 Market-Condition restricted stock units 12,989 1.2 ESPP 3,743 0.7 Total unrecognized stock-based compensation expense $ 166,009 2.5

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Defined Contribution Plan	11. Defined Contribution Plan In 2013, we began to sponsor a 401(k) retirement plan, in which substantially all of our full-time employees are eligible to participate. Eligible participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. We made contributions to the Plan for eligible participants, and recorded contribution expenses of $2.1 million for the year ended December 31, 2020, $1.4 million for the year ended December 31, 2019, and $0.8 million for the year ended December 31, 2018.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The components of the loss before income taxes were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Loss before provision for income taxes: United States $ (247,327 ) $ (266,595 ) $ (174,190 ) International (226 ) (167 ) — $ (247,553 ) $ (266,762 ) $ (174,190 ) No provision for income taxes was recorded for the years ended December 31, 2020, December 31, 2019, and December 31, 2018. We have incurred net operating losses for all the periods presented. We have not reflected any benefit of such net operating loss (NOL) carryforwards in the accompanying consolidated financial statements. We have established a full valuation allowance against the related deferred tax assets due to the uncertainty surrounding the realization of such assets. The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2020 2019 2018 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % State taxes 7.4 9.7 1.3 Federal and state tax credits 4.3 4.9 7.1 Change in valuation allowance (32.4 ) (37.2 ) (33.3 ) Foreign rate differential — — 1.7 Officer compensation limitation (0.8 ) (1.0 ) (0.7 ) Stock based compensation/Non-deductible 0.6 1.7 2.9 Liquidation of foreign entities — 0.9 — Other (0.1 ) — — Provision for Taxes 0.0 % 0.0 % 0.0 % The components of the deferred tax assets and liabilities are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 216,092 $ 157,685 Tax credits 76,684 62,862 Operating lease liability 23,147 16,177 Accruals and reserves 6,503 3,996 Stock based compensation 14,981 11,166 Intangibles 8,507 8,243 Other 904 408 Gross deferred tax assets 346,818 260,537 Valuation allowance (325,710 ) (245,000 ) Net deferred tax assets 21,108 15,537 Operating lease – ROU asset (13,975 ) (14,971 ) Property and equipment (7,050 ) (352 ) Other (83 ) (214 ) Gross deferred tax liabilities (21,108 ) (15,537 ) Net deferred tax assets $ — $ — Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. We have established a valuation allowance to offset deferred tax assets as of December 31, 2020 and 2019 due to the uncertainty of realizing future tax benefits from our net operating loss carryforwards and other deferred tax assets. The valuation allowance increased approximately and December 31, 2020, and 2019, respectively. As of December 31, 2020, we had federal net operating loss carryforwards of approximately $829.1 million to offset future federal taxable income, with $209.9 million available through 2037 and $619.2 million available indefinitely. We also had state net operating loss carryforwards of approximately $587.1 million that may offset future state taxable income through 2040. Current federal and state tax laws include substantial restrictions on the utilization of net operating losses and tax credits in the event of an ownership change. Even if the carryforwards are available, they may be subject to annual limitations, lack of future taxable income, or future ownership changes that could result in the expiration of the carryforwards before they are utilized. At December 31, 2020, we recorded a 100% valuation allowance against our deferred tax assets of approximately $325.7 million, as at that time our management believed it was uncertain that they would be fully realized. If we determine in the future that we will be able to realize all or a portion of our net operating loss carryforwards, an adjustment to valuation allowance would increase net income in the period in which we make such a determination. In general, if we experience a greater than 50 percentage point aggregate change in ownership over a three-year period (a Section 382 ownership change), utilization of our pre-change tax-exempt No liability related to uncertain tax positions is recorded on the consolidated financial statements. All uncertain tax positions are currently recorded as a reduction to our deferred tax asset. It is our policy to include A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): December 31, 2020 2019 Balance at beginning of year $ 21,598 $ 16,232 Additions based on tax positions related to current year 3,346 5,366 Decreased for prior period positions (498 ) — Unrecognized tax benefit—December 3 1 $ 24,446 $ 21,598 We do not expect that our uncertain tax positions will materially change in the next twelve months. The reversal of the uncertain tax benefits will not impact our effective tax rate as we continue to maintain a full valuation allowance against our deferred tax assets. We file federal, state and foreign income tax returns in the United States and in multiple foreign jurisdictions. We are not currently under examination by income tax authorities in federal, state or other jurisdictions. All tax returns will remain open for examination by the federal and state authorities for three and four years, respectively, from the date of utilization of any net operating loss or credits.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss per Share	13. Net Loss per Share Basic net loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding for the period. Since we were in a loss position for all periods presented, diluted net loss per share is the same as basic net loss per share for all periods as the inclusion of all potential common shares outstanding would have been anti-dilutive. The following securities were not included in the diluted net loss per share calculations because their effect was anti-dilutive: December 31, 2020 2019 2018 Options to purchase common stock 3,327,330 3,573,860 3,243,551 Restricted shares subject to future vesting — — 47,051 Restricted stock units 2,625,056 1,848,772 975,419 Total 5,952,386 5,422,632 4,266,021

Selected Quarterly Financial In

Selected Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	Selected Quarterly Financial Information (unaudited) The following table provides the selected consolidated quarterly financial data for 2020 and 2019: Quarter Ended (in thousands, except per share December 31, September 30, June 30, March 31, December 31, September 30, June 30, March 31, Product sales, net $ 41,295 $ 36,889 $ 31,501 $ 14,118 $ 2,108 $ — $ — $ — Loss from operations $ (59,373 ) $ (58,311 ) $ (52,036 ) $ (73,452 ) $ (99,214 ) $ (68,742 ) $ (60,804 ) $ (52,523 ) Net loss $ (61,806 ) $ (59,881 ) $ (52,840 ) $ (73,026 ) $ (95,975 ) $ (64,547 ) $ (57,321 ) $ (48,923 ) Basic and diluted net loss per common share $ (1.00 ) $ (0.97 ) $ (0.86 ) $ (1.20 ) $ (1.59 ) $ (1.07 ) $ (1.01 ) $ (0.87 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP.
Use of Estimates	Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of variable consideration and costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances have been eliminated upon consolidation.
Accruals of Research and Development and Manufacturing Costs	Accruals of Research and Development and Manufacturing Costs We record accruals for estimated costs of research, nonclinical and clinical studies and manufacturing development. These costs are a significant component of our research and development expenses. A substantial portion of our ongoing research and development activities are conducted by third-party service providers, including contract research organizations and contract manufacturing organizations. We also accrue for estimated costs of manufacturing activities for inventories. These costs are a significant component of the cost of our inventory. We accrue the costs incurred under our agreements with these third parties based on actual work completed in accordance with agreements established with these third parties. We determine the accruals for research and development costs through discussions with internal personnel and external service providers as to the progress or stage of completion of the clinical studies and the agreed-upon fee to be paid for such services. The accrual for contract manufacturing activities is based on an estimate of manufacturing activities completed to date, contractual rates, and amounts invoiced and paid to date at the end of each reporting period. We determine the percentage of manufacturing activities completed to date based on discussions with the contract manufacturing organizations , oversight of the manufacturing activities and anticipated timeline. As actual costs become known, we adjust our accruals. We have not experienced any material deviations between accrued costs and actual costs. However, actual clinical and manufacturing services performed, number of subjects enrolled, and the rate of subject enrollment may vary from our estimates, resulting in adjustments to research and development costs or inventories in future periods. Changes in these estimates that result in material changes to our accruals of research and development and manufacturing costs could materially affect our results of operations or amounts of inventories capitalized.
Segment Reporting	Segment Reporting We have determined that we operate in a single segment based upon the way the business is organized for making operating decisions and assessing performance. We have only one operating segment related to the development of pharmaceutical products. All property and equipment is maintained in the United States.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents, which consist primarily of amounts invested in money market accounts, are stated at fair value.
Investments in Marketable Securities	Investments in Marketable Securities We invest in marketable securities, primarily money market funds, corporate debt securities, government securities, government agency securities, and certificates of deposits. We classify our marketable securities as available-for-sale available-for-sale available-for-sale We regularly review all of our investments for other-than-temporary declines in estimated fair value. Our review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether we have the intent to sell the securities and whether it is more likely than not that we will be required to sell the securities before the recovery of their amortized cost basis. When we determine that the decline in estimated fair value of an investment is below the amortized cost basis and the decline is other than temporary, we reduce the carrying value of the security and record a loss for the amount of such decline.
Fair Value Measurement	Fair Value Measurement The carrying amounts of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Concentration of Risk	Concentration of Risk Credit Risk We invest in a variety of financial instruments and, by our Board approved investment policy, limit the amount of credit exposure with any one issuer, industry or geographic area for investments other than instruments backed by the U.S. federal government. Major Customers We have entered into distribution agreements with certain limited specialty pharmacies and a specialty distributor. For the year ended December 31, 2020, our two largest customers represented approximately 92% of our product revenue and approximately 88% of our accounts receivable balance at December 31, 2020. Major Suppliers We do not currently have any of our own manufacturing facilities, and therefore depend on an outsourced manufacturing strategy for the production of Oxbryta for commercial use and for the production of our product candidates for clinical trials. We have contracts in place with one third-party manufacturer that is approved for the commercial production of Oxbryta and two third-party suppliers that are approved for Oxbryta’s active pharmaceutical ingredient. Although there are potential sources of supply other than our existing manufacturers and suppliers, any new supplier would be required to qualify under applicable regulatory requirements.
Accounts Receivables, net	Accounts Receivables, net Accounts receivables are recorded net of estimates of variable consideration for which reserves are established and which result from discounts and chargebacks that are offered within contracts between us and a limited number of specialty pharmacies and a specialty distributor in the United States. These reserves are classified as reductions of accounts receivable. We estimate the allowance for doubtful accounts using current expected credit loss model, or CECL model. Under the CECL model, the allowance for doubtful accounts reflects the net amount expected to be collected from the account receivables. We evaluate the collectability of these cash flow based on the asset’s amortized cost, the risk of loss even when that risk is remote, losses over an asset’s contractual life, and other relevant information available to us. Accounts receivable balances are written off against the allowance when it is probable that the receivable will not be collected. Given the nature and history of our accounts receivable, we determined that an allowance for doubtful accounts was not required at December 31, 2020.
Inventories	Inventories Inventories are stated at the lower of cost or estimated net realizable value, on a first-in, work-in-process, We began capitalizing costs as inventory when the product candidate received regulatory approval. Prior to regulatory approval, we recorded inventory costs related to product candidates as research and development expenses. We periodically assess the recoverability of our inventory and reduce the carrying value of the inventory when items are determined to be obsolete, defective or in excess of forecasted sales requirements. Inventory write-downs for excess, defective and obsolete inventory are recorded as a cost of sales. There have been no write-downs of our inventories for the periods presented.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which is three years for computer equipment and five years for laboratory equipment. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begins at the time the asset is placed in service. Maintenance and repairs are charged as expense in the statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheet and any resulting gain or loss is reflected in operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows the asset is expected to generate over its remaining life. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset. There have been no impairments of our long-lived assets for the periods presented.
Restricted Cash	Restricted Cash Restricted cash consists of cash deposits held by our financial institution as collateral for our letter of credit under our facility lease.
Revenue Recognition	Revenue Recognition Pursuant to Accounting Standards Codification, Topic 606, Revenue from Contracts with Customers , To determine revenue recognition for arrangements that we determine are within the scope of ASC 606, we perform the following five steps: (i) identify the contract(s) 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 in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation. We only apply the five-step model to contracts when it is probable that we will collect substantially all of the consideration we are entitled to in exchange for the goods or services we transfer to the customer. Product sales, net Our product sales consist of U.S. sales of Oxbryta, which we began shipping to customers in December 2019. Prior to December 2019, we had no product sales. We sell Oxbryta to a limited number of specialty pharmacies and a specialty distributor, or collectively, Customers. These agreements with our Customers provide for transfer of title to the product at the time the product has been delivered to the Customers. The Customers subsequently dispense our products directly to a patient or resell our products to hospitals and certain pharmacies. We recognize revenue on product sales when the Customers obtain control of our product, which occurs at a point in time, typically upon delivery to our Customers. It is at that point that we have a right to payment and that our Customers obtain title and the risks and rewards of ownership. Shipping and handling activities are considered to be fulfillment activities rather than a separate performance obligation. Payment terms are typically 30-60 We consider the effects of items that can decrease the transaction price, such as variable consideration and consideration payable to Customers or payer. Amounts related to such items are estimated at contract inception and updated at the end of each reporting period as additional information becomes available. The amount of variable consideration may be constrained and is included in the transaction price only to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Revenue from product sales is recorded after considering the impact of the following variable consideration amounts along with the constraint at the time of revenue recognition: Rebates: Prompt payment discounts Co-payment co-payment co-payment co-payment co-payment Medicare Part D Coverage Gap: Product returns: Chargebacks chargebacks in the same period that the related revenue is recognized, resulting in a reduction of product revenue and receivables. Distributor fees: Other revenue recognition considerations Oxbryta is our only product. The only performance obligation included in our contracts is the delivery of Oxbryta to our Customers. Therefore, no allocation of transaction price amongst performance obligations is necessary. Consequently, the transaction price determined after considering the impacts of variable consideration is recognized at the time control is transferred to our Customers, which is upon delivery of Oxbryta to our Customers. Because all sales of Oxbryta are in the United States and because our Customers are each a large distributor with similar variable consideration impacts, we provide revenue numbers on a total basis without further disaggregation. Additionally, we do not have any contract assets or liabilities, other than accounts receivable, related to our sales of Oxbryta.
Cost of Sales	Cost of Sales Cost of sales consists primarily of direct and indirect costs related to the manufacturing of Oxbryta products sold, including third-party manufacturing costs, packaging services, freight, storage costs, allocation of overhead costs of employees involved with production, and Oxbryta net sales-based royalties payable to the Regents of the University of California. Costs incurred prior to FDA approval of Oxbryta in November 2019 have been recorded as research and development expense in our consolidated statement of operations and comprehensive loss.
Leases	Leases Pursuant to Accounting Standards Codification, Topic 842, Leases adopted on January 1, 2019 , Right-of-use, As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the commencement date in determining the present value of future payments. We consider our credit risk, term of the lease, and total lease payments and adjust for the impact of collateral, as necessary, when calculating our incremental borrowing rates. The lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. Lease cost for our operating leases is recognized on a straight-line basis over the lease term. We have elected to not separate lease and non-lease non-lease ROU assets and operating lease liabilities are remeasured upon certain modifications to leases using the present value of remaining lease payments and estimated incremental borrowing rate upon lease modification. Leases (Topic 840) Prior to the Adoption of Topic 842 We enter into lease agreements for our office and laboratory facilities. These leases are classified as operating leases. Rent expense is recognized on a straight-line basis over the noncancelable term of the lease and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability, which is included within other liabilities on the consolidated balance sheet. Incentives granted under our facilities leases, including rent holiday and allowances to fund leasehold improvements, are deferred and are recognized as adjustments to rental expense on a straight-line basis over the noncancelable term of the lease.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner
Research and Development	Research and Development Research and development costs are expensed as incurred and consist of salaries and benefits, stock-based compensation expense, lab supplies and facility costs, as well as fees paid to other nonemployees and entities that conduct certain research and development activities on our behalf. Amounts incurred in connection with license agreements are also included in research and development expense. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and then expensed as the related goods are delivered or the services are performed.
Long-term Debt	Long-term Debt Long-term debt consists of our loan agreement, or Term Loan, with funds managed by Pharmakon Advisors LP, which are BioPharma Credit PLC, as collateral agent and a lender, and Biopharma Credit Investments V (Master) LP, as a lender, and collectively, the Lenders. We accounted for the Term Loan as a debt financing arrangement. Interest expense is accrued using the effective interest rate method over the estimated period the debt will be repaid. Debt issuance costs have been recorded as a debt discount in our consolidated balance sheets and are being amortized and recorded as interest expense throughout the life of the Term Loan using the effective interest rate method. We consider whether there are any embedded features in our debt instruments that require bifurcation and separate accounting as derivative financial instruments pursuant to Accounting Standards Codification, or ASC, Topic 815, Derivatives and Hedging There are no embedded features identified from our Term Loan that require bifurcation and separating accounting.
Stock-based Compensation	Stock-Based Compensation We measure and recognize stock-based compensation expense, including employee and non-employee
Income Taxes	Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. We recognize benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. It is our policy to include penalties and interest expense related to income taxes as a component of other expense and interest expense, respectively, as necessary. To date, there have been no interest or penalties incurred in relation to the unrecognized tax benefits.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given our net loss.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes 2019-12 Accounting Pronouncements Adopted In August 2018, FASB, issued ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use 350-40), Arrangement That Is a Service Contract 2018-15. No. 2018-15 internal-use 350-40 No. 2018-15 In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) No. 2018-13 No. 2018-13 In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments (Topic 326) U.S. GAAP an impairment model that is based on expected losses rather than incurred losses, which is known as the current expected credit loss, or CECL model. The CECL model applies to most debt instruments (other than those measured at fair value), trade and other receivables, financial guarantee contracts, and loan commitments. Available-for-sale available-for-sale No. 2016-13

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	The following table summarizes our financial assets measured at fair value on a recurring basis (in thousands): December 31, 2020 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 486,174 $ 486,174 $ — $ — Corporate debt securities 29,804 — 29,804 — U.S. government agency securities 15,943 — 15,943 — Certificates of deposits 243 — 243 — U.S. government securities 20,136 — 20,136 — Total financial assets $ 552,300 $ 486,174 $ 66,126 $ — December 31, 2019 Total Level 1 Level 2 Level 3 Financial Assets: Money market funds $ 250,535 $ 250,535 $ — $ — Corporate debt securities 152,149 — 152,149 — U.S. government agency securities 95,032 — 95,032 — Certificates of deposits 6,282 — 6,282 — U.S. government securities 140,244 — 140,244 — Total financial assets $ 644,242 $ 250,535 $ 393,707 $ —

Available-for-Sale Securities (

Available-for-Sale Securities (Tables)	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities	The following table is a summary of available-for-sale December 31, 2020 December 31, 2019 Amortized Unrealized Unrealized Estimated Amortized Unrealized Unrealized Estimated Financial Assets: Money market funds $ 486,174 $ — $ — $ 486,174 $ 250,535 $ — $ — $ 250,535 Corporate debt securities 29,641 163 — 29,804 151,773 384 (8 ) 152,149 U.S. government agency securities 15,906 37 — 15,943 94,963 73 (4 ) 95,032 Certificates of deposits 241 2 — 243 6,239 43 — 6,282 U.S. government securities 20,036 100 — 20,136 139,978 266 — 140,244 Total $ 551,998 $ 302 $ — $ 552,300 $ 643,488 $ 766 $ (12 ) $ 644,242
Summary of Classification of Available-for-Sale Securities on Consolidated Balance Sheets	The following table summarizes the classification of the available-for-sale c b s December 31, December 31, Cash and cash equivalents $ 486,174 $ 251,480 Short-term marketable securities 66,126 307,732 Long-term marketable securities — 85,030 Total $ 552,300 $ 644,242

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Property and Equipment, Net	Property and equipment consist of the following (in thousands): December 31, 2020 2019 Laboratory equipment $ 11,922 $ 8,314 Computer equipment 3,023 2,224 Leasehold improvements 32,281 13,785 Construction-in-progress 517 19,289 Total property and equipment 47,743 43,612 Less: accumulated depreciation and amortization (9,861 ) (16,499 ) Property and equipment, net $ 37,882 $ 27,113
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): December 31, 2020 2019 Accrued research and development costs $ 10,677 $ 26,480 Accrued manufacturing costs 9,125 9,466 Accrued professional and consulting services 4,107 4,564 Accrued sales deductions 6,405 529 Other 819 319 Total accrued liabilities $ 31,133 $ 41,358
Other Liabilities	Other liabilities consist of the following (in thousands): December 31, 2020 2019 Operating lease liabilities, current $ 4,836 $ 1,866 Other payable — 30 Total other liabilities, current $ 4,836 $ 1,896

Inventories (Table)

Inventories (Table)	12 Months Ended
	Dec. 31, 2020
Disclosure Text Block [Abstract]
Inventories	We began capitalizing inventories in November December 31, 2020 2019 Raw materials $ 11,273 $ 700 Work-in-process 26,994 525 Finished goods 1,956 52 Total inventories $ 40,223 $ 1,277

Long-term Debt (Table)

Long-term Debt (Table)	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Schedule of Future payments of principal and interest on the Term Loan	Future payments of principal and interest on the Term Loan as of December 31, 2020 (in thousands): 2021 13,500 2022 13,500 2023 62,813 2024 58,313 2025 53,812 Total minimum payments 201,938 Less amount representing interest (48,938 ) Less amount representing Paydown Fee (3,000 ) Long-term debt, gross 150,000 Discount on notes payable (1,596 ) Accretion of Paydown Fee 411 Long-term debt $ 148,815

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Summary of supplemental information related to leases	Supplemental information related to leases for the period reported is as follows (in thousands, except weighted-average remaining lease term and weighted-average discount rate): For the year ended 2020 2019 ROU assets obtained in exchange for new operating lease upon adoption of ASC 842 $ — $ 14,177 Adjustment to ROU assets as a result of the lease modification for the Prior Premises (106 ) (13,802 ) ROU assets obtained for new operating lease liabilities 205 53,727 Operating lease liabilities arising from obtaining ROU assets 205 25,929 Cash paid for amounts included in the measurement of lease liabilities 7,696 4,481 Weighted-average remaining lease term of operating leases (in years) 9.2 10.1 Weighted-average discount rate of operating leases 8.66 % 8.66 %
Schedule of Lessee, Operating Lease, Liability, Maturity	As of December 31, 2020, the maturities of our operating lease liabilities under Topic 842 were as follows (in thousands): Year ending December 31, Amount 2021 11,841 2022 12,222 2023 12,584 2024 12,948 2025 13,368 Thereafter 60,507 Total lease payments 123,470 Less: Imputed interest (39,458 ) Present value of operating lease liabilities $ 84,012

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Common Stock Reserved For Future Issuance	We have reserved shares of common stock for future issuance as follows: December 31, 2020 2019 Restricted stock units 2,625,056 1,848,772 Options issued and outstanding 3,327,330 3,573,860 Shares available for future grant under the 2015 Plan and 2017 Inducement Equity Plan 6,018,567 4,478,656 Employee stock purchase plan 254,590 252,655 Total 12,225,543 10,153,943

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Stock Option Activity	The following table summarizes activity under our stock option plans, including the 2017 Inducement Plan, 2015 Plan and the 2012 Plan and related information (in thousands, except share and per share amounts and term): Number Weighted- Weighted- Aggregate Outstanding—December 31, 2019 3,573,860 $ 36.24 7.55 Options granted 719,561 65.36 Options exercised (525,788 ) 25.35 Options canceled (440,303 ) 52.78 Outstanding—December 31, 2020 3,327,330 $ 42.07 7.02 $ 29,720 Vested and exercisable—December 31, 2020 2,151,326 $ 34.77 6.33 $ 28,616
Valuation Assumptions for Stock Awards	The fair values of stock options granted to employees were calculated using the following assumptions: Year Ended December 31, 2020 2019 2018 Expected term (in years) 5.1-6.1 5.3-6.1 5.3-6.1 Volatility 69.6%-71.8% 69.8%-72.2% 68.7%-71.8% Risk-free interest rate 0.3%-1.8% 1.4%-2.6% 2.6%-3.0% Dividend yield — — —
Stock-based Compensation Expense Recognized	Total stock-based compensation recognized by functions was as follows (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 18,061 $ 19,140 $ 12,747 Selling, general and administrative 53,416 26,511 17,333 Total stock-based compensation expense $ 71,477 $ 45,651 $ 30,080
Unrecognized Stock-based Compensation Cost	As of December 31, 2020, the unrecognized stock-based compensation cost, and the estimated weighted-average amortization period, using the straight-line attribution method, was as follows (in thousands, except amortization period): Unrecognized Compensation Weighted- remaining amortization Stock $ 38,440 2.3 Restricted stock units 110,837 2.7 Market-Condition restricted stock units 12,989 1.2 ESPP 3,743 0.7 Total unrecognized stock-based compensation expense $ 166,009 2.5
Summary of Share-based Compensation Arrangements by Share-based Payment Award	Stock Price Targets Number of Units Allotted $109.20 82,940 $145.60 145,145 $182.00 186,615
Restricted Stock Units [Member]
Non-Vested Restricted Stock Activity	The following table summarizes activity of RSUs granted to employees with service-based vesting under the 2017 Inducement Plan and 2015 Plan and related information (in thousands, except share, per share amounts and vesting period): Number Weighted- Weighted- Aggregate Non-vested 1,848,772 $ 49.19 1.54 $ 146,959 RSUs granted 1,577,047 64.28 RSUs vested (710,403 ) 50.84 RSUs forfeited (505,060 ) 56.30 Non-vested 2,210,356 $ 57.80 1.45 $ 95,731
Market Condition Awards Granted to Employees [Member]
Summary of Activity of Market-Condition Awards	The following table summarizes activity of the 2020 Market-Condition RSU Awards under the 2015 Plan and related information (in thousands, except share, per share amounts and vesting period): Number Weighted- Weighted- Aggregate Non-vested — $ — — Granted 421,000 49.95 Vested — — Forfeited (6,300 ) 49.95 Non-vested 414,700 $ 49.95 1.21 $ 17,961
Valuation Assumptions of Market-Condition Awards	The following table summarizes the assumptions used to estimate the fair value of the market-condition awards as of the grant date: Valuation date stock price $ 68.67 Volatility 68.1 % Risk-free interest rate 0.26 % Dividend yield —
ESPP [Member]
Fair Value Assumptions for Employee Stock Purchase Plan	The fair values of the rights granted under the 2015 ESPP were calculated using the following assumptions: Year Ended Year Ended Expected term (in years) 0.5 – 2.1 0.5 – 2.0 Volatility 47.0-77.0 % 46.5-75.4 % Risk-free interest rate 0.1-1.5 % 1.7-2.6 % Dividend yield — % — %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Loss Before Income Taxes	The components of the loss before income taxes were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Loss before provision for income taxes: United States $ (247,327 ) $ (266,595 ) $ (174,190 ) International (226 ) (167 ) — $ (247,553 ) $ (266,762 ) $ (174,190 )
Effective Income Tax Rate Reconciliation	The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows: Year Ended December 31, 2020 2019 2018 Federal statutory income tax rate 21.0 % 21.0 % 21.0 % State taxes 7.4 9.7 1.3 Federal and state tax credits 4.3 4.9 7.1 Change in valuation allowance (32.4 ) (37.2 ) (33.3 ) Foreign rate differential — — 1.7 Officer compensation limitation (0.8 ) (1.0 ) (0.7 ) Stock based compensation/Non-deductible 0.6 1.7 2.9 Liquidation of foreign entities — 0.9 — Other (0.1 ) — — Provision for Taxes 0.0 % 0.0 % 0.0 %
Components of Deferred Tax Assets and Liabilities	The components of the deferred tax assets and liabilities are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 216,092 $ 157,685 Tax credits 76,684 62,862 Operating lease liability 23,147 16,177 Accruals and reserves 6,503 3,996 Stock based compensation 14,981 11,166 Intangibles 8,507 8,243 Other 904 408 Gross deferred tax assets 346,818 260,537 Valuation allowance (325,710 ) (245,000 ) Net deferred tax assets 21,108 15,537 Operating lease – ROU asset (13,975 ) (14,971 ) Property and equipment (7,050 ) (352 ) Other (83 ) (214 ) Gross deferred tax liabilities (21,108 ) (15,537 ) Net deferred tax assets $ — $ —
Reconciliation of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): December 31, 2020 2019 Balance at beginning of year $ 21,598 $ 16,232 Additions based on tax positions related to current year 3,346 5,366 Decreased for prior period positions (498 ) — Unrecognized tax benefit—December 3 1 $ 24,446 $ 21,598

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Potentially Dilutive Securities that were Not Included in Diluted Net Loss per Share Calculations	The following securities were not included in the diluted net loss per share calculations because their effect was anti-dilutive: December 31, 2020 2019 2018 Options to purchase common stock 3,327,330 3,573,860 3,243,551 Restricted shares subject to future vesting — — 47,051 Restricted stock units 2,625,056 1,848,772 975,419 Total 5,952,386 5,422,632 4,266,021

Selected Quarterly Financial _2

Selected Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information (Unaudited)	The following table provides the selected consolidated quarterly financial data for 2020 and 2019: Quarter Ended (in thousands, except per share December 31, September 30, June 30, March 31, December 31, September 30, June 30, March 31, Product sales, net $ 41,295 $ 36,889 $ 31,501 $ 14,118 $ 2,108 $ — $ — $ — Loss from operations $ (59,373 ) $ (58,311 ) $ (52,036 ) $ (73,452 ) $ (99,214 ) $ (68,742 ) $ (60,804 ) $ (52,523 ) Net loss $ (61,806 ) $ (59,881 ) $ (52,840 ) $ (73,026 ) $ (95,975 ) $ (64,547 ) $ (57,321 ) $ (48,923 ) Basic and diluted net loss per common share $ (1.00 ) $ (0.97 ) $ (0.86 ) $ (1.20 ) $ (1.59 ) $ (1.07 ) $ (1.01 ) $ (0.87 )

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Cumulative net losses	$ 986,469	$ 738,916

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - Customer Concentration Risk [Member] - Two Major Customers [Member]	12 Months Ended
	Dec. 31, 2020
Revenue, Product and Service Benchmark [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	92.00%
Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	88.00%

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Assets Measured on Recurring Basis (Detail) - Fair Value Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	$ 552,300	$ 644,242
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	20,136	140,244
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	486,174	250,535
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	66,126	393,707
Level 2 [Member] | U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	20,136	140,244
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	486,174	250,535
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	486,174	250,535
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	29,804	152,149
Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	29,804	152,149
U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	15,943	95,032
U.S. Government Agency Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	15,943	95,032
Certificates of Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	243	6,282
Certificates of Deposits [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets, fair value	$ 243	$ 6,282

Available-for-Sale Securities -

Available-for-Sale Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	$ 551,998	$ 643,488
Available for sale securities, Unrealized Gains	302	766
Available for sale securities, Unrealized (Losses)		(12)
Available for sale securities, Estimated Fair Value	552,300	644,242
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	29,641	151,773
Available for sale securities, Unrealized Gains	163	384
Available for sale securities, Unrealized (Losses)		(8)
Available for sale securities, Estimated Fair Value	29,804	152,149
U.S. Government Agency Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	15,906	94,963
Available for sale securities, Unrealized Gains	37	73
Available for sale securities, Unrealized (Losses)		(4)
Available for sale securities, Estimated Fair Value	15,943	95,032
Money Market Funds [Member]
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	486,174	250,535
Available for sale securities, Estimated Fair Value	486,174	250,535
Certificates of Deposits [Member]
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	241	6,239
Available for sale securities, Unrealized Gains	2	43
Available for sale securities, Estimated Fair Value	243	6,282
U.S. Government Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available for sale securities, Amortized Cost	20,036	139,978
Available for sale securities, Unrealized Gains	100	266
Available for sale securities, Estimated Fair Value	$ 20,136	$ 140,244

Available-for-Sale Securities_2

Available-for-Sale Securities - Summary of Classification of Available-for-Sale Securities on Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents	$ 486,174	$ 251,480
Short-term marketable securities	66,126	307,732
Long-term marketable securities		85,030
Total	$ 552,300	$ 644,242

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 47,743	$ 43,612
Less: accumulated depreciation and amortization	(9,861)	(16,499)
Property and equipment, net	37,882	27,113
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	11,922	8,314
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,023	2,224
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	32,281	13,785
Construction-in-Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 517	$ 19,289

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Components [Abstract]
Depreciation expense	$ 8.3	$ 8.6	$ 4.7

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Accrued research and development costs	$ 10,677	$ 26,480
Accrued manufacturing costs	9,125	9,466
Accrued professional and consulting services	4,107	4,564
Accrued sales deductions	6,405	529
Other	819	319
Total accrued liabilities	$ 31,133	$ 41,358

Balance Sheet Components - Othe

Balance Sheet Components - Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Operating lease liabilities, current	$ 4,836	$ 1,866
Other payable		30
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Total other liabilities, current	$ 4,836	$ 1,896

Inventories - Summary of Capita

Inventories - Summary of Capitalizing Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory, Raw Materials and Supplies, Gross [Abstract]
Raw materials	$ 11,273	$ 700
Work-in-process	26,994	525
Finished goods	1,956	52
Total inventories	$ 40,223	$ 1,277

Inventories - Additional inform

Inventories - Additional information (Detail) $ in Millions	Dec. 31, 2020USD ($)
Disclosure Text Block [Abstract]
Share-based Compensation	$ 1.8

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Nov. 30, 2020	Nov. 20, 2020	Dec. 31, 2019	Dec. 17, 2019
Long term debt	$ 148,815			$ 73,559
Secured Debt
Debt maximum borrowing capacity					$ 75,000
Debt additional borrowing capacity					$ 75,000
Long term debt			$ 75,000	$ 75,000
Unamortized dedt discount		$ 200
Term Loan
Debt additional borrowing capacity	$ 75,000
Debt Instrument, Term	72 months
Debt Instrument, Basis Spread on Variable Rate	7.00%
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	2.00%
Debt Instrument Additional Interest Rate On Debt Default	3.00%
Debt Instrument Periodic Payment Of Interest	Interest on amounts outstanding are payable quarterly in arrears
Debt Instrument Periodic Payment Of Interest Term	39 months
Debt additional paydown fee	2.00%
Debt issuance costs paid	$ 1,100
Other debt issuance cost paid	500
Unamortized issuance costs and debt discounts	1,300
Debt additional paydown fee	$ 1,100
Term Loan | Maximum
Debt prepayment fee	3.00%
Term Loan | Minimum
Debt prepayment fee	1.00%

Long-term Debt-Schedule of Futu

Long-term Debt-Schedule of Future payments of principal and interest on the Term Loan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Contractual Obligation, Fiscal Year Maturity Schedule [Abstract]
2021	$ 13,500
2022	13,500
2023	62,813
2024	58,313
2025	53,812
Total minimum payments	201,938
Less amount representing interest	(48,938)
Less amount representing Paydown Fee	(3,000)
Long-term debt, gross	150,000
Discount on notes payable	(1,596)
Accretion of Paydown Fee	411
Long-term debt	$ 148,815	$ 73,559

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Aug. 31, 2018USD ($)ft²	Mar. 31, 2017ft²	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Oct. 01, 2019USD ($)
Commitment And Contingencies [Line Items]
Facility size | ft²	164,150	67,185
Initial term		10 years
Future minimum rental payments under the Lease term	$ 121,500,000
Operating lease term	10 years
Operating lease term, optional extension	10 years
Repayment of tenant inducement allowance	$ 4,100,000
Contingency losses			$ 0
Provisions for loss contingency			0
Operating Lease Cost			12,400,000	$ 7,800,000
variable lease cost			2,600,000	2,500,000
Rent expense			9,800,000	5,200,000	$ 3,600,000
Operating liabilities			84,012,000			$ 2,900,000
Operating lease liabilities			$ 84,012,000			$ 2,900,000
Incremental borrowing rate			8.66%			8.78%
Operating lease right of use asset			$ 50,722,000	52,775,000		$ 0
Gain loss on modification of lease			984,000	8,301,000
Unamortized operating lease liability			0	1,800,000
Tenant inducement allowances received			10,700,000	17,200,000
Depreciation expense			8,300,000	8,600,000	$ 4,700,000
Substitute Premises [Member]
Commitment And Contingencies [Line Items]
Operating liabilities			83,800,000	72,400,000		53,700,000
Operating lease liabilities			83,800,000	72,400,000		53,700,000
Operating lease right of use asset			50,600,000	52,800,000		$ 53,700,000
F. Hoffmann-La Roche Ltd. And Hoffmann-La Roche Inc. [Member]
Commitment And Contingencies [Line Items]
Upfront payments			2,000,000
Contingent payment obligations			125,500,000
Contingent Payment Milestone Additional Obligations			6,400,000
F. Hoffmann-La Roche Ltd. And Hoffmann-La Roche Inc. [Member] | Develpment And Regulatory Milestones [Member]
Commitment And Contingencies [Line Items]
Contingent Payment Milestone Additional Obligations			19,250,000
F. Hoffmann-La Roche Ltd. And Hoffmann-La Roche Inc. [Member] | Net Sales Achievement [Member]
Commitment And Contingencies [Line Items]
Contingent payment obligations			85,000,000
F. Hoffmann-La Roche Ltd. And Hoffmann-La Roche Inc. [Member] | Research And Development Milestones [Member]
Commitment And Contingencies [Line Items]
Contingent payment obligations			40,500,000
Contingent Payment Milestone Additional Obligations			2,000,000
Syros Pharmaceuticals [Member]
Commitment And Contingencies [Line Items]
Upfront payments			20,000,000
Preclinical research payable			40,000,000
Payable for exercise of options			315,000,000
Repayment of Research and Development Cost			8,600,000
Syros Pharmaceuticals [Member] | Research And Development Milestones [Member]
Commitment And Contingencies [Line Items]
Contingent Payment Milestone Additional Obligations			$ 0
Maximum [Member]
Commitment And Contingencies [Line Items]
Lease term			10 years
Minimum [Member]
Commitment And Contingencies [Line Items]
Lease term			1 year
Leasehold Improvements [Member]
Commitment And Contingencies [Line Items]
Property palnt and equipment additions			$ 32,300,000	19,000,000
Depreciation expense			$ 3,800,000	$ 7,000,000
Lease Agreements [Member] | Maximum [Member]
Commitment And Contingencies [Line Items]
Tenant inducement	$ 27,900,000

Commitments and Contingencies_2

Commitments and Contingencies - Supplemental cash flow information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Oct. 01, 2019
Commitment And Contingencies [Line Items]
Weighted-average discount rate of operating leases	8.66%		8.78%
Accounting Standards Update 2016-02 [Member]
Commitment And Contingencies [Line Items]
ROU assets obtained in exchange for new operating lease upon adoption of ASC 842	$ 0	$ 14,177
Adjustment to ROU assets as a result of the lease modification for the Prior Premises	(106)	(13,802)
ROU assets obtained for new operating lease liabilities	205	53,727
Operating lease liabilities arising from obtaining ROU assets	205	25,929
Cash paid for amounts included in the measurement of lease liabilities	$ 7,696	$ 4,481
Weighted-average remaining lease term of operating leases (in years)	9 years 2 months 12 days	10 years 1 month 6 days
Weighted-average discount rate of operating leases	8.66%	8.66%

Commitments and Contingencies_3

Commitments and Contingencies - Lessee Operating Lease Liability Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Oct. 01, 2019
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2021	$ 11,841
2022	12,222
2023	12,584
2024	12,948
2025	13,368
Thereafter	60,507
Total lease payments	123,470
Less: Imputed interest	(39,458)
Present value of operating lease liabilities	$ 84,012	$ 2,900

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended				12 Months Ended
	Jul. 31, 2019	Jun. 30, 2019	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock dividend declared					$ 0
Issuance of common stock upon equity offerings, net of issuance costs, Shares		3,375,527		3,409,090
Common Stock Issue Price	$ 57.12	$ 57.12	$ 41.54	$ 41.54			$ 41.54
Proceeds from Issuance of Common Stock,Net of Expenses	$ 5,700,000	$ 192,400,000	$ 21,200,000	$ 141,100,000		$ 219,443,000	$ 396,501,000
Shares Issued to Underwriters due to execise their Over Allotment Option	100,000		511,363

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Issuance on Converted basis (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Shares reserved for future issuance	12,225,543	10,153,943
RSU [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	2,625,056	1,848,772
Stock Options [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	3,327,330	3,573,860
Shares Available for Future Grant Under the 2015 Plan and 2017 Inducement Equity Plan [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	6,018,567	4,478,656
ESPP [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	254,590	252,655

Share-based Compensation - Plan

Share-based Compensation - Plan Summary - Additional Information (Detail) - USD ($)	Aug. 11, 2017	Jul. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance | shares			12,225,543	10,153,943
Intrinsic value of options exercised			$ 23,000,000	$ 23,500,000	$ 23,400,000
Estimated weighted-average grant-date fair value of common stock underlying options granted			$ 40.76	$ 32.30	$ 33.58
Dividend yield			0.00%
Unrecognized compensation expense			$ 166,009,000
weighted average derived service period			2 years 6 months
Stock-based compensation			$ 71,477,000	$ 45,651,000	$ 30,080,000
Shares issued, value			$ 4,137,000	$ 2,361,000	$ 1,647,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance | shares			3,327,330	3,573,860
Dividend yield			0.00%	0.00%	0.00%
weighted average derived service period			2 years 3 months 18 days
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance | shares			254,590	252,655
Dividend yield			0.00%	0.00%
weighted average derived service period			8 months 12 days
RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance | shares			2,625,056	1,848,772
weighted average derived service period			2 years 8 months 12 days
Market Condition Awards Granted to Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense			$ 13,000,000
weighted average derived service period			1 year 2 months 15 days
Stock-based compensation			$ 7,700,000
2017 Market-Condition RSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ 0	$ 36,500	$ 3,100,000
Number of shares vesting Period				156,000
Number of shares forfeited				3,250
Number of shares Non-vested period			0	0
2017 Inducement Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance			1,277,475
2017 Inducement Equity Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period			10 years
Exercise price as a percentage of the fair market value			100.00%
2017 Inducement Equity Plan [Member] | Stock Options [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Vesting Percentage			25.00%
2017 Inducement Equity Plan [Member] | Stock Options [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
2017 Inducement Equity Plan [Member] | RSU [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage			25.00%
2017 Inducement Equity Plan [Member] | RSU [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
2015 Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance | shares			4,741,092
Expiration period			10 years
Exercise price as a percentage of the fair market value			100.00%
Exercise price as a percentage of the fair market value for option holding more than 10% total combined voting power			110.00%
Vesting period			4 years
2015 Plan [Member] | Market Condition Awards Granted to Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted in period			421,000
Number of shares vesting Period			0
Number of shares forfeited			6,300
Number of shares Non-vested period			414,700	0
2015 Plan [Member] | 2017 Market-Condition RSU Awards [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted in period	365,250
2015 Plan [Member] | 2020 Market-Condition RSU Awards [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares granted in period			414,700
2012 Stock Option and Grant Plan [Member] | ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period			10 years
2015 ESPP [Member] | ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price as a percentage of the fair market value		85.00%
Maximum contribution to plan as a percent of employee's eligible compensation		15.00%
2015 Inducement Equity Plan [Member] | Stock Options [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage			6.25%
2015 Inducement Equity Plan [Member] | RSU [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Vesting Percentage			12.50%
2015 Inducement Equity Plan [Member] | RSU [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage			12.50%
2015 ESPAP [Member] | ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued			98,065
Shares issued, value			$ 4,100,000

Share-based Compensation - Stoc

Share-based Compensation - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, outstanding, Number of Options	3,573,860
Options granted, Number of Options	719,561
Options exercised, Number of Options	(525,788)
Options canceled, Number of Options	(440,303)
Ending balance, outstanding, Number of Options	3,327,330	3,573,860
Vested and exercisable, Number of Options	2,151,326
Weighted- Average Exercise Price
Beginning balance, Outstanding, Weighted-Average Exercise Price	$ 36.24
Options granted, Weighted-Average Exercise Price	65.36
Options exercised, Weighted-Average Exercise Price	25.35
Options canceled, Weighted-Average Exercise Price	52.78
Ending balance, Outstanding, Weighted-Average Exercise Price	42.07	$ 36.24
Vested and exercisable, Weighted-Average Exercise Price	$ 34.77
Beginning, Outstanding, Weighted-Average remaining contractual term	7 years 7 days	7 years 6 months 18 days
Vested and exercisable, Weighted-Average remaining contractual term	6 years 3 months 29 days
Balance Outstanding, Aggregate Intrinsic Value	$ 29,720
Vested and exercisable, Aggregate Intrinsic Value	$ 28,616

Share-based Compensation - Valu

Share-based Compensation - Valuation Assumptions for Stock Options Granted (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, minimum	69.60%	69.80%	68.70%
Volatility, maximum	71.80%	72.20%	71.80%
Risk-free interest rate, minimum	0.30%	1.40%	2.60%
Risk-free interest rate, maximum	1.80%	2.60%	3.00%
Dividend yield	0.00%	0.00%	0.00%
Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 1 month 6 days	5 years 3 months 18 days	5 years 3 months 18 days
Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Share-based Compensation - Summ

Share-based Compensation - Summary of RSU Activity Granted to Employees with Service-Based Vesting (Detail) - 2017 Inducement Plan and 2015 Plan [Member] - RSU [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance - Non-vested market-condition awards	1,848,772
RSUs granted, Number of RSUs	1,577,047
RSUs vested, Number of RSUs	(710,403)
RSUs forfeited, Number of RSUs	(505,060)
Ending Balance - Non-vested market-condition awards	2,210,356	1,848,772
Beginning Balance - Non-vested units, Weighted-Average Grant Date Fair Value	$ 49.19
RSUs granted, Weighted-Average Grant Date Fair Value	64.28
RSUs vested, Weighted-Average Grant Date Fair Value	50.84
RSUs forfeited, Weighted-Average Grant Date Fair Value	56.30
Ending Balance - Non-vested units, Weighted-Average Grant Date Fair Value	$ 57.80	$ 49.19
Non-vested units, Weighted-Average remaining vesting period(years)	1 year 5 months 12 days	1 year 6 months 14 days
Non-vested units, Aggregate Intrinsic Value	$ 95,731	$ 146,959

Share-based Compensation - Su_2

Share-based Compensation - Summary of Share-based Compensation Arrangements by Share-based Payment Award (Detail)	Dec. 31, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Price Targets	$ 34.77
Tranche One [Member] | 2020 Market Condition RSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Price Targets	$ 109.20
Number of Units Allotted | shares	82,940
Tranche Two [Member] | 2020 Market Condition RSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Price Targets	$ 145.60
Number of Units Allotted | shares	145,145
Tranche Three [Member] | 2020 Market Condition RSU Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Price Targets	$ 182
Number of Units Allotted | shares	186,615

Share-based Compensation - Su_3

Share-based Compensation - Summary of Activity of Market-Condition Awards (Detail) - Market Condition Awards Granted to Employees [Member] - 2015 Plan [Member] $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance - Non-vested market-condition awards | shares	0
Number of Units granted | shares	421,000
Number of Units vested | shares	0
Number of Units forfeited | shares	(6,300)
Ending Balance - Non-vested market-condition awards | shares	414,700
Beginning Balance - Non-vested units, Weighted-Average Grant Date Fair Value | $ / shares	$ 0
Weighted-Average Grant Date Fair Value granted | $ / shares	49.95
Weighted-Average Grant Date Fair Value vested | $ / shares	0
Weighted-Average Grant Date Fair Value forfeited | $ / shares	49.95
Ending Balance - Non-vested units, Weighted-Average Grant Date Fair Value | $ / shares	$ 49.95
Non-vested units, Weighted-Average remaining vesting period(years)	1 year 2 months 15 days
Non-vested units, Aggregate Intrinsic Value | $	$ 17,961

Share-based Compensation - Va_2

Share-based Compensation - Valuation Assumptions of Market-Condition Awards (Detail) - Market Condition Awards Granted To Employees [Member]	12 Months Ended
	Dec. 31, 2020$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Valuation date stock price	$ 68.67
Volatility	68.10%
Risk-free interest rate	0.26%
Dividend yield	0.00%

Share-based Compensation - Fair

Share-based Compensation - Fair Value Assumptions for Employee Stock Purchase Plan (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, minimum	47.00%	46.50%
Volatility, maximum	77.00%	75.40%
Risk-free interest rate, minimum	0.10%	1.70%
Risk-free interest rate, maximum	1.50%	2.60%
Dividend yield	0.00%	0.00%
ESPP [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	2 years 1 month 6 days	2 years
ESPP [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months

Share-based Compensation - St_2

Share-based Compensation - Stock-based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 71,477	$ 45,651	$ 30,080
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	18,061	19,140	12,747
Selling, general and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 53,416	$ 26,511	$ 17,333

Stock-based Compensation - Unre

Stock-based Compensation - Unrecognized Stock-based Compensation Cost (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense	$ 166,009
Weighted-average remaining amortization period	2 years 6 months
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, options	$ 38,440
Weighted-average remaining amortization period	2 years 3 months 18 days
RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, restricted stock awards	$ 110,837
Weighted-average remaining amortization period	2 years 8 months 12 days
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, restricted stock awards	$ 3,743
Weighted-average remaining amortization period	8 months 12 days
Market-Condition RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, restricted stock awards	$ 12,989
Weighted-average remaining amortization period	1 year 2 months 12 days

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Contribution expenses	$ 2.1	$ 1.4	$ 0.8

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Increase in valuation allowance	80,700,000	99,200,000
Deferred tax assets, valuation allowance	$ 325,710,000	$ 245,000,000
valuation allowance charged on deferred tax assets	100.00%
State [Member]
Income Taxes [Line Items]
Operating loss carry forward, expiration year	2040
State [Member] | Operating Loss Carryforward Expiration Year 2040 [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 587,100,000
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 829,100,000
Operating loss carry forward, expiration year	2037
Domestic Tax Authority [Member] | Tax period 2037 [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 209,900,000
Domestic Tax Authority [Member] | Operating Loss Carryforward With Indefinite Expiry Period [Member]
Income Taxes [Line Items]
Operating loss carryforwards	$ 619,200,000

Income Taxes - Components of Lo

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss before provision for income taxes:
United States	$ (247,327)	$ (266,595)	$ (174,190)
International	(226)	(167)
Loss before provision for income taxes	$ (247,553)	$ (266,762)	$ (174,190)

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Reconciliation (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	21.00%
State taxes	7.40%	9.70%	1.30%
Federal and state tax credits	4.30%	4.90%	7.10%
Change in valuation allowance	(32.40%)	(37.20%)	(33.30%)
Foreign rate differential			1.70%
Officer compensation limitation	(0.80%)	(1.00%)	(0.70%)
Stock based compensation/Non-deductible changes in fair value	0.60%	1.70%	2.90%
Liquidation of foreign entities	0.00%	0.90%
Other	(0.10%)
Provision for Taxes	0.00%	0.00%	0.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 216,092	$ 157,685
Tax credits	76,684	62,862
Operating lease liability	23,147	16,177
Accruals and reserves	6,503	3,996
Stock based compensation	14,981	11,166
Intangibles	8,507	8,243
Other	904	408
Gross deferred tax assets	346,818	260,537
Valuation allowance	(325,710)	(245,000)
Net deferred tax assets	21,108	15,537
Operating lease – ROU asset	(13,975)	(14,971)
Property and equipment	(7,050)	(352)
Other	(83)	(214)
Gross deferred tax liabilities	(21,108)	(15,537)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 21,598	$ 16,232
Additions based on tax positions related to current year	3,346	5,366
Decreased for prior period positions	(498)
Unrecognized tax benefit - December 31	$ 24,446	$ 21,598

Net Loss per Share - Potentiall

Net Loss per Share - Potentially Dilutive Securities that were Not Included in Diluted Net Loss per Share Calculations (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share	5,952,386	5,422,632	4,266,021
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share	3,327,330	3,573,860	3,243,551
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share			47,051
RSU [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from earnings per share	2,625,056	1,848,772	975,419

Selected Quarterly Financial _3

Selected Quarterly Financial Information (Unaudited) - Selected Consolidated Quarterly Financial Information (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Product sales, net	$ 41,295	$ 36,889	$ 31,501	$ 14,118	$ 2,108
Loss from operations	(59,373)	(58,311)	(52,036)	(73,452)	(99,214)	$ (68,742)	$ (60,804)	$ (52,523)	$ (243,172)	$ (281,283)	$ (182,742)
Net loss	$ (61,806)	$ (59,881)	$ (52,840)	$ (73,026)	$ (95,975)	$ (64,547)	$ (57,321)	$ (48,923)	$ (247,553)	$ (266,766)	$ (174,193)
Basic and diluted net loss per common share	$ (1)	$ (0.97)	$ (0.86)	$ (1.20)	$ (1.59)	$ (1.07)	$ (1.01)	$ (0.87)	$ (4.04)	$ (4.57)	$ (3.41)