Molecular Templates (MTEM) 10-Q 6 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 02, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	MTEM
Entity Registrant Name	Molecular Templates, Inc.
Entity Central Index Key	0001183765
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-32979
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3409596
Entity Address, Address Line One	9301 Amberglen Blvd
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Austin
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78729
City Area Code	512
Local Phone Number	869-1555
Entity Common Stock, Shares Outstanding		49,964,219
Title of 12(b) Security	Common Stock, $0.001 Par Value Per Share
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 33,410	$ 85,451
Marketable securities, current	82,816	39,633
Prepaid expenses	4,889	2,318
Grants revenue receivable	3,490	7,100
Accounts receivable, related party	301	408
In-process research and development - held for sale	4,500	4,500
Other current assets	249	489
Total current assets	129,655	139,899
Marketable securities, non-current	2,000	1,510
Operating lease right-of-use assets, non-current	11,589	9,959
Property and equipment, net	20,889	18,158
Other assets	5,244	4,676
Total assets	169,377	174,202
Current liabilities:
Accounts payable	2,565	1,465
Accrued liabilities	13,231	14,544
Deferred revenue, current	12,496	8,511
Deferred revenue, current, related party	4,566	8,780
Other current liabilities, related party	5,498	0
Other current liabilities	2,041	2,501
Total current liabilities	40,397	35,801
Deferred revenue, long-term	7,785	18,944
Deferred revenue, long-term, related party	935	441
Long-term debt, net	14,822	2,940
Operating lease liabilities, non-current	12,828	11,682
Other liabilities, related party	6,711	0
Other liabilities	1,458	1,366
Total liabilities	84,936	71,174
Commitments and contingencies (Note 10)	0	0
Stockholders’ equity
Preferred stock, $0.001 par value: Authorized: 2,000,000 shares at September 30, 2020 and December 31, 2019; issued and outstanding: 250 shares at September 30, 2020 and December 31, 2019	0	0
Common stock, $0.001 par value: Authorized: 150,000,000 shares at September 30, 2020 and December 31, 2019; issued and outstanding: 49,963,732 shares at September 30, 2020 and 45,589,157 shares at December 31, 2019	50	46
Additional paid-in capital	324,914	267,089
Accumulated other comprehensive income	73	18
Accumulated deficit	(240,596)	(164,125)
Total stockholders’ equity	84,441	103,028
Total liabilities and stockholders’ equity	$ 169,377	$ 174,202

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	250	250
Preferred stock, shares outstanding	250	250
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	49,963,732	45,589,157
Common stock, shares outstanding	49,963,732	45,589,157

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total revenue	$ 4,298,000	$ 3,618,000	$ 15,348,000	$ 16,073,000
Operating expenses:
Research and development	19,622,000	15,249,000	70,667,000	33,946,000
General and administrative	7,547,000	4,509,000	19,606,000	14,049,000
Loss on impairment of in-process research and development	0	22,123,000	0	22,123,000
Total operating expenses	27,169,000	41,881,000	90,273,000	70,118,000
Loss from operations	22,871,000	38,263,000	74,925,000	54,045,000
Interest and other income, net	167,000	396,000	925,000	1,449,000
Interest and other expense, net	(521,000)	(353,000)	(1,229,000)	(947,000)
Loss on extinguishment of debt	0	0	(1,237,000)	0
Change in fair value of warrant liabilities	0	1,000	0	3,000
Loss before provision for income taxes	23,225,000	38,219,000	76,466,000	53,540,000
Provision for income taxes	0	0	5,000	0
Net loss	23,225,000	38,219,000	76,471,000	53,540,000
Net loss attributable to common shareholders	$ 23,225,000	$ 38,219,000	$ 76,471,000	$ 53,540,000
Net loss per share attributable to common shareholders:
Basic and diluted	$ 0.47	$ 1.03	$ 1.63	$ 1.45
Weighted average number of shares used in net loss per share calculations:
Basic and diluted	49,026,499	36,937,912	46,808,437	36,832,966
Research And Development Revenue | Other
Total revenue	$ 2,732,000	$ 284,000	$ 7,176,000	$ 284,000
Research And Development Revenue | Related Party
Total revenue	1,566,000	2,903,000	4,962,000	14,527,000
Grant
Total revenue	$ 0	$ 431,000	$ 3,210,000	$ 1,262,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ 23,225	$ 38,219	$ 76,471	$ 53,540
Other comprehensive income:
Unrealized gain, (loss) on available-for-sale securities	(99)	(5)	55	20
Comprehensive loss	$ 23,324	$ 38,224	$ 76,416	$ 53,520

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 100,906	$ 0	$ 37	$ 195,573	$ 0	$ (94,704)
Issuance of preferred stock		0
Issuance of common stock pursuant to stock plans			0	1,300
Stock-based compensation				4,330
Issuance of common stock pursuant to Public offering				0
Other comprehensive income					20
Net loss	(53,540)					(53,540)
Ending balance at Sep. 30, 2019	53,016	0	37	201,203	20	(148,244)
Beginning balance at Jun. 30, 2019	89,260	0	37	199,223	25	(110,025)
Issuance of preferred stock		0
Issuance of common stock pursuant to stock plans			0	453
Stock-based compensation				1,527
Issuance of common stock pursuant to Public offering				0
Other comprehensive income					(5)
Net loss	(38,219)					(38,219)
Ending balance at Sep. 30, 2019	53,016	0	37	201,203	20	(148,244)
Beginning balance at Dec. 31, 2019	103,028	0	46	267,089	18	(164,125)
Issuance of preferred stock		0
Issuance of common stock pursuant to stock plans			4	930
Stock-based compensation				8,527
Issuance of common stock pursuant to Public offering				48,368
Other comprehensive income					55
Net loss	(76,471)					(76,471)
Ending balance at Sep. 30, 2020	84,441	0	50	324,914	73	(240,596)
Beginning balance at Jun. 30, 2020	55,859	0	46	273,012	172	(217,371)
Issuance of preferred stock		0
Issuance of common stock pursuant to stock plans			4	249
Stock-based compensation				3,285
Issuance of common stock pursuant to Public offering				48,368
Other comprehensive income					(99)
Net loss	(23,225)					(23,225)
Ending balance at Sep. 30, 2020	$ 84,441	$ 0	$ 50	$ 324,914	$ 73	$ (240,596)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ 76,471	$ 53,540
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and other	2,526	628
Stock-based compensation expense	8,527	4,330
Interest accrued (paid) on long-term debt	106	0
Amortization of debt discount and accretion related to debt	344	347
Change in common stock warrant fair value	0	(3)
Accretion of asset retirement obligations	93	48
Loss on extinguishment of debt	1,237	0
Loss on impairment of long-lived assets	0	22,139
Changes in operating assets and liabilities:
Prepaid expenses	(2,571)	(96)
Accounts receivable, related party	107	240
Grants revenue receivable	3,610	(1,262)
Other assets	301	(145)
Operating lease right-of-use assets and liabilities	(129)	566
Accounts payable	644	524
Accrued liabilities	(1,930)	2,661
Other liabilities, related party	12,209	0
Deferred revenue	(7,174)	0
Deferred revenue, related party	(3,720)	(15,709)
Net cash used in operating activities	(62,291)	(39,272)
Cash flows from investing activities:
Purchases of property and equipment	(4,512)	(6,329)
Proceeds on sale of equipment	15	0
Purchase of marketable securities	(115,895)	(73,758)
Sales of marketable securities	72,523	48,583
Net cash used in investing activities	(47,869)	(31,504)
Cash flows from financing activities:
Payments of capital and finance lease obligations	(16)	23
Proceeds from issuance of long-term debt and warrants, net	14,677	0
Repayment of long-term debt	(5,176)	0
Proceeds from stock option exercises	930	1,300
Proceeds from issuance of common stock and warrants, net of offering expenses	48,372	0
Net cash provided by financing activities	58,787	1,323
Net (decrease) in cash, cash equivalents, and restricted cash	(51,373)	(69,453)
Cash, cash equivalents and restricted cash, beginning of period	88,451	87,721
Cash, cash equivalents and restricted cash, end of period	37,078	18,268
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	33,410	15,268
Restricted cash included in Other assets	$ 3,668	$ 3,000
Restricted Cash and Cash Equivalents, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Cash, cash equivalents and restricted cash, end of period	$ 37,078	$ 18,268
Supplemental Cash Flow Information
Cash paid for interest	611	514
Non-Cash Investing and Financing Activities
Fixed asset additions in accounts payable and accrued expenses	967	1,197
Total non-cash investing and financing activities	$ 967	$ 1,197

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	NOTE 1 — ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of the Business Molecular Templates, Inc. (the “Company”) is a clinical stage biopharmaceutical company formed in 2001, with a biologic therapeutic platform for the development of novel targeted therapeutics for cancer and other diseases, headquartered in Austin, Texas. The Company’s focus is on the research and development of therapeutic compounds for a variety of cancers. The Company operates its business as a single segment, as defined by U.S. generally accepted accounting principles (“U.S. GAAP”). On August 1, 2017, the Company, formerly known as Threshold Pharmaceuticals, Inc. (Nasdaq: THLD) (“Threshold”), completed its business combination with Private Molecular, in accordance with the terms of the Agreement and Plan of Merger and Reorganization (the “Merger Agreement”), dated as of March 16, 2017, by and among Threshold, the Merger Sub, a wholly owned subsidiary of Threshold, and Private Molecular, pursuant to which Merger Sub merged with and into Private Molecular, with Private Molecular, surviving as a wholly-owned subsidiary of Threshold (the “Merger”). Immediately upon completion of the Merger, the former stockholders of Private Molecular held a majority of the voting interest of the combined company. In March 2020, the outbreak of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), or the novel coronavirus, which causes the coronavirus disease 2019 (“COVID-19”) was recognized as a pandemic by the World Health Organization. While the COVID-19 pandemic has not had a material adverse impact on the Company’s operations to date, it has resulted in a significant slowdown in the pace of site initiations and patient enrollment across the Company’s MT-3724 Phase II programs. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, including its ongoing clinical trials, results of operations and financial condition will depend on future developments that are highly uncertain. Additionally, the economic impact of COVID-19 on local, regional, national and international markets may have a material adverse impact on the Company. Refer to Item 1A. “Risk Factors” in this Quarterly Report on Form 10-Q for a complete description of risks. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America and include the accounts of the Company and its wholly owned subsidiary, and reflect the elimination of intercompany accounts and transactions. The preparation of condensed consolidated financial statements requires management to make estimates and assumptions that affect the recorded amounts reported therein. The business and economic uncertainty resulting from the COVID-19 pandemic has made such estimates and assumptions more difficult to calculate. Accordingly, actual results and outcomes could differ from those estimates, and a change in facts or circumstances surrounding the estimates could result in a change to estimates and impact future operating results. The unaudited condensed consolidated financial statements and related disclosures have been prepared with the presumption that users of the interim unaudited condensed consolidated financial statements have read or have access to the audited consolidated financial statements for the preceding fiscal year. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 13, 2020. Reclassifications Certain amounts in the prior year’s presentation have been reclassified to conform to the current presentation. The condensed consolidated balance sheet at December 31, 2019 included herein was derived from the audited financial statements at that date, but includes a reclassification of $8.8 million from Deferred revenue, current to Deferred revenue, current, related party and $0.4 million from Deferred revenue, non-current to Deferred revenue, non-current, related party in order to conform to current period presentation. The condensed consolidated statements of cash flow for the nine months ended September 30, 2019, included herein includes a reclassification of $12.7 million from Deferred revenue to Deferred revenue, related party. Liquidity At September 30, 2020, we had cash, cash equivalents, and marketable securities of $118.2 million. The Company has devoted substantially all of its resources to developing its ETB candidates and platform technology, building its intellectual property portfolio, developing its supply chain, conducting business planning, raising capital and providing for general and administrative support for these operations. The Company expects that its existing cash, cash equivalents and marketable securities will enable it to fund its operating expenses and capital expenditure requirements into the second half of 2022. Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2020, as compared to the significant accounting policies disclosed in Note 1, Summary of significant accounting policies, to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. Cash and Cash Equivalents The Company considers temporary investments having original maturities of three months or less from date of purchase to be cash equivalents. Restricted cash is recorded in other assets, based on when the restrictions expire. Other assets includes $3.7 million of restricted cash at September 30, 2020 and $3.0 million at December 31, 2019. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash and cash equivalents are with two major financial institutions in the United States. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. The Company’s exposure to credit risk associated with non-payment will be affected principally by conditions or occurrences within Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda Pharmaceutical Company Ltd. (“Takeda”) and Vertex Pharmaceuticals Incorporated (“Vertex”) In July 2020, the Company became aware of one potentially non-conforming batch of a single Company product fill, which may not meet manufacturing specifications. The Company continues to investigate the batch. The Company continues to investigate the batch. If upon the conclusion of the batch evaluation such batch is deemed to be non-conforming this could result in a reversal of revenue in future periods as the Company recognizes collaboration revenue over time by measuring toward completion to satisfy the performance obligation. The Company does not believe this potential non-conforming batch will result in an increased timeline for its ongoing projects nor does it affect any other batches, production, or manufacturing. The Company expects to be able to meet the supply needs for all of its active clinical trials. Drug or biologic candidates developed by the Company may require approvals or clearances from the U.S. Food and Drug Administration (“FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug or biologic candidates will receive any of the required approvals or clearances. If the Company were to be denied approval or clearance or any such approval or clearance were to be delayed, it would have a material adverse impact on the Company. Recently Issued Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (“ In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). ASU 2018-15 aligns the accounting for implementation costs incurred in a hosting arrangement that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. This ASU was effective for annual periods beginning after December 15, 2019, including interim periods within that period, and early adoption is permitted. The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC Topic 606 when the counterparty is a customer. In addition, Topic 808 precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance was effective for the Company beginning January 1, 2020 . The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses, which requires recognizing credit losses on financial instruments based on an estimate of current expected credit losses. The new guidance applies to loans, accounts receivable, trade receivables, other financial assets measured at amortized cost, loan commitments and other off-balance sheet credit exposures. The new guidance also applies to debt securities and other financial assets measured at fair value through other comprehensive income. This guidance was effective for the Company beginning January 1, 2020 . The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740: Simplifying the Accounting for Income Taxes), which removes certain exceptions to the general principles in Topic 740. ASU 2019-12 is effective for the fiscal years beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848: Facilitation of the Effects of Reference Rate Reform on Financial Reporting). The new guidance provides optional guidance for a limited period of time for applying U.S. GAAP to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. The guidance will be effective prospectively as of March 12, 2020 through December 31, 2022 and interim periods within those fiscal years. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2020, the FASB issued ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (Subtopic 470-20: Debt with Conversion and Other Options and Subtopic 815-40: Derivatives and Hedging— Contracts in Entity’s Own Equity). The new guidance simplifies accounting for convertible instruments by removing major separation models, removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception and it also simplifies the diluted earnings per share calculation in certain areas. The amendment is effective for the Company for fiscal years beginning after December 15, 2023. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Common Share	NOTE 2 — NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing net loss by the weighted-average number of common shares outstanding during the period utilizing the two-class method. Preferred Stock Shareholders participate equally with Common Stock Shareholders in earnings, but do not participate in losses, and are excluded from the basic net loss calculation. Diluted net loss per share is computed by giving effect to all potential dilutive common shares, including outstanding options, warrants and convertible preferred stock. More specifically, at September 30, 2020 and 2019 stock options, warrants and, if converted, preferred stock totaling approximately 9,996,000 and 8,121,000 common shares, respectively, were excluded from the computation of diluted net loss per share as their effect would have been anti-dilutive.

Research and Development Agreem

Research and Development Agreements	9 Months Ended
	Sep. 30, 2020
Research And Development [Abstract]
Research and Development Agreements	NOTE 3 — RESEARCH AND DEVELOPMENT AGREEMENTS Disaggregated Research and Development Revenue Research and development revenue is attributable to regions based on the location of the Company’s collaboration partner's parent company headquarters. Research and development revenues disaggregated by location were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Japan $ 1,566 $ 2,903 $ 4,962 $ 14,527 United States 2,732 284 7,176 284 Total research and development revenue $ 4,298 $ 3,187 $ 12,138 $ 14,811 Related Party Collaboration Agreement - Takeda Research and development revenue from related party relates to revenue from research and development agreements with Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda and were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Takeda Individual Project Agreement $ — $ — $ — $ 54 Takeda Development and License Agreement 86 2,581 307 13,707 Takeda Multi-Target Agreement 1,480 322 4,655 766 Total research and development revenue, related party $ 1,566 $ 2,903 $ 4,962 $ 14,527 At September 30, 2020 and December 31, 2019, the Company had deferred revenue, other liabilities for co-share payments and accounts receivable balances from the research and development agreements with Takeda, who is a related party. These amounts were as follows (in thousands): September 30, 2020 December 31, 2019 Assets Accounts receivable $ 301 $ 408 Liabilities Other current liabilities $ 5,498 — Deferred revenue, current 4,566 8,780 Deferred revenue, non-current 935 441 Other liabilities 6,711 — Total liabilities $ 17,710 $ 9,221 Takeda Development and License Agreement On September 18, 2018, the Company entered into a Development Collaboration and Exclusive License Agreement with Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda (“Takeda Development and License Agreement”), for the development and commercialization of products incorporating or comprised of one or more CD38 SLT-A fusion proteins (“Licensed Products”) for the treatment of patients with diseases such as multiple myeloma. The Company, at its discretion, exercised its co-development option in July 2019 and as a result is eligible to receive pre-clinical and clinical development milestone payments of up to $307.5 million upon the achievement of certain development milestones and regulatory approvals, and sales milestone payments of up to $325.0 million upon the achievement of certain sales milestone events. The Company may elect to end its co-development by providing Takeda with written notice of termination of the co-development. In the event the Company elects to end the co-development, the Company will be subject to reduced payments and royalty rates as set forth more specifically in the Takeda Development and License Agreement. The Company will also be entitled to receive tiered royalties, subject to certain reductions, as percentages of annual aggregate net sales, if any, of Licensed Products. The royalty percentages would range from low double-digits to low twenties following the Company’s exercise of its option to co-develop, and from high-single digits to low teens if the Company elects to end its co-development. The Company identified one performance obligation at the inception of the Takeda Development and License Agreement, the research and development services for the CD38-targeted SLT-A fusion protein, including manufacturing. The Company determined that research, development and commercialization license and the participation in the committee meetings are not distinct from the research and development services and therefore those promised services were combined into one combined performance obligation. The total transaction price of $29.8 million consists of (1) the $30.0 million upfront payment, (2) a $10.0 million development milestone payment that was received in the first quarter of 2020, (3) minus $10.2 million in expected co-share payment payable to Takeda during Early Stage Development, as defined in the Takeda Development and License Agreement. The expected co-share payment is considered variable consideration, and the Company applied a constraint using the expected value method. Significant judgement was involved in determining transaction consideration, including the determination of the variable consideration, including the constraint on consideration. A t September 30, 2020 , the other potential development milestones and sales milestones were not currently deemed probable of being achieved, as they are dependent on factors outside the Company ’ s control . Therefore, these future development milestones and sales-based milestone payments have been fully constrained and are not included in the transaction price. The Company recognizes revenue using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company used actual costs incurred relative to budgeted costs expected to be incurred for the combined performance obligation. These costs consist primarily of internal employee efforts and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the estimated service period. In July 2019, the Company exercised its co-development option and the agreed upon collaboration budget was increased to cover additional research and development activities whereby both parties will continue to cost share . At September 30, 2020 and December 31, 2019, total deferred revenue related to the performance obligation was $2.7 million and $6.1 million, respectively. Takeda Multi-Target Agreement In June 2017, the Company entered into a Multi-Target Collaboration and License Agreement with Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda (the “Takeda Multi-Target Agreement”), in which the Company agreed to collaborate with Takeda to identify and generate ETBs, against two targets designated by Takeda. Takeda designated certain targets of interest as the focus of the research. Each party granted to the other nonexclusive rights in its intellectual property for purposes of the conduct of the research, and the Company agreed to work exclusively with Takeda with respect to the designated targets. Under the Takeda Multi-Target Agreement, Takeda has an option during an option period to obtain an exclusive license under the Company’s intellectual property to develop, manufacture, commercialize and otherwise exploit ETBs against the designated targets. The option period for each target ends three months after the completion of the evaluation of such designated target. As of September 30, 2020, the Company has received cumulative payments of $5.0 million from Takeda pursuant to the Takeda Multi-Target Agreement. The Company may receive additional payments from the following: • $30.0 million in aggregate through the exercise of the option to license ETBs. • Clinical development milestone payments of up to approximately $397.0 million, for achievement of development milestones and regulatory approval of collaboration products under the Takeda Multi-Target Agreement. • C ommercial milestone payments of up to $150.0 million, for achievement of pre-specified sales milestones related to net sales of all collaboration products under the Takeda Multi-Target Agreement. • Tiered royalty payments of a mid-single to low-double digit percentage of net sales of any licensed ETBs, subject to certain reductions. • Up to $10.0 million in certain contingency fees. The Takeda Multi-Target Agreement will expire on the expiration of all option periods (three months after the completion of the evaluation of materials for the designated targets) for the designated targets if Takeda does not exercise its options, or, following exercise of any option, on the expiration of the last Royalty Term (the latest of the expiration of patent rights claiming the licensed ETB, expiration of regulatory exclusivity for the licensed ETB or ten years from first commercial sale of the licensed ETB). The Takeda Multi-Target Agreement may be terminated sooner by Takeda for convenience or upon a material change of control of the Company, or by either party for an uncured material breach of the agreement. Under the Takeda Multi-Target Agreement, both parties have the right to terminate the agreement immediately upon written notice, under certain defined circumstances. The Company evaluated the Takeda Multi-Target Agreement’s termination clause and concluded that it was a non-substantive termination provision. As such, the Company believes that an initial contract term is the length of the termination notice period, with a deemed renewal option to continue the research and development services over the remainder of the contract term as a material right. The Company determined that the promised goods and services under the Takeda Multi-Target Agreement were the background intellectual property license, the research and development services, manufacturing during the initial contract period, and a renewal option to continue the research and development services. The Company determined that there were two performance obligations: research and development services, and the renewal options. Since the background intellectual property and manufacturing were not distinct from the research and development services, they were deemed to be one performance obligation. Transaction consideration was allocated to each of the performance obligations using an estimate of the standalone selling price, and revenues are recognized over the period that the research and development services occur. The Company also concluded that, since the option for the exclusive license is deemed to be at fair value, the option does not provide the customer with a material right and should be accounted for if and when the option is exercised. At September 30, 2020 and December 31, 2019, deferred revenue related to the performance obligation was $2.8 million and $3.1 million, respectively. Vertex Collaboration Agreement In November 2019, the Company entered into a Master Collaboration Agreement (the “Vertex Collaboration Agreement”) with Vertex, to perform strategic research leveraging the Company’s ETB technology platform to discover and develop novel targeted biologic therapies for applications outside of oncology. Pursuant to the terms of the Vertex Collaboration Agreement, the Company granted Vertex an exclusive option to obtain an exclusive license under the Company’s licensed technology to exploit one or more ETB products that are discovered by the Company against up to two designated targets. Vertex has selected an initial target and has the option to designate one additional target within specified time limits. Vertex paid the Company an upfront payment of $38 million, consisting of $23 million in cash and a $15 million equity investment pursuant to a Share Purchase Agreement (the “SPA”), described below. In addition to the upfront payments, the Company may also receive an additional $22 million through the exercise of the options to license ETB products or to add an additional target. Additionally, Vertex will reimburse the Company for certain mutually agreed manufacturing technology transfer activities. The Company may, for each target under the Vertex Collaboration Agreement, receive up to an additional $180 million in milestone payments upon the achievement of certain development and regulatory milestone events and up to an additional $70 million in milestone payments upon the achievement of certain sales milestone events. The Company will also be entitled to receive, subject to certain reductions, tiered mid-single digit royalties as percentages of calendar year net sales, if any, on any licensed product. The Company will be responsible for conducting the research activities through the designation, if any, of one or more development candidates. Upon the exercise by Vertex of its option for a development candidate, Vertex will be responsible for all development, manufacturing, regulatory and commercialization activities with respect to that development candidate. Unless earlier terminated, the Vertex Collaboration Agreement will expire (i) on a country-by-country basis and licensed product-by-licensed product basis on the date of expiration of all payment obligations under the Vertex Collaboration Agreement with respect to such licensed product in such country and (ii) in its entirety upon the expiration of all payment obligations thereunder with respect to all licensed products in all countries or upon Vertex’s decision not to exercise any option on or prior to the applicable deadlines. Vertex has the right to terminate the Vertex Collaboration Agreement for convenience upon prior written notice to the Company. Either party has the right to terminate the Vertex Collaboration Agreement (a) for the insolvency of the other party or (b) subject to specified cure periods, in the event of the other party’s uncured material breach. The Company identified one performance obligation at the inception of the Vertex Collaboration Agreement consisting of research and development services. The Company recognizes revenue under the Vertex Collaboration Agreement using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company will use actual costs incurred relative to budgeted costs expected to be incurred. These costs consist primarily of internal employee efforts and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the estimated service period. In connection with the Vertex Collaboration Agreement, the Company and Vertex entered into a SPA pursuant to which Vertex agreed to purchase 1,666,666 shares of the Company’s common stock, par value $0.001 per share, at a price per share of $9.00. As the price per share was in excess of the fair value of the Company’s common stock, the Company allocated $4.5 million of this consideration to the Vertex Collaboration Agreement. The issuance of these shares was pursuant to a private placement exemption from registration afforded by Section 4(a)(2) of the Securities Act of 1933, as amended, and Rule 506 of Regulation D thereunder. In addition to the SPA, the Vertex Collaboration Agreement contemplates that the Company may enter into certain other ancillary arrangements with Vertex. At September 30, 2020 and December 31, 2019, deferred revenue related the Vertex Collaboration Agreement was $20.3 million and $27.5 million, respectively. Grant Agreements I n September 2018, the Company entered into a Cancer Research Agreement (the “CD38 CPRIT Agreement”) with the Cancer Prevention and Research Institute of Texas (“ was extended in October 2020, under which CPRIT awarded a to fund research of a cancer therapy involving a CD38 targeting ETB Pursuant to the CD38 CPRIT Agreement, the Company may also use such funds to develop a replacement CD38 targeting ETB, with or without a partner. In 2011, the Company entered into a Cancer Research Agreement (the “CPRIT Agreement”) with CPRIT under which CPRIT awarded a $10.6 million product development grant for the CD20-targeting ETB MT-3724. This product development grant ended in November 2019. At September 30, 2020, the Company had received $16.4 million and has a remaining receivable of $3.5 million. During the three months ended September 30, 2020 and September 30, 2019, the Company recognized no revenue and $0.4 million in grant revenue under these awards, respectively. , respectively, recorded in Grants revenue receivable.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	NOTE 4 — RELATED PARTY TRANSACTIONS Takeda Agreements In connection with the Takeda Multi-Target Agreement described in Note 3 “Research and Development Collaboration Agreements”, Takeda became a related party, following the Takeda Stock Purchase Agreement described in Note 11 “Stockholders’ Equity”, of the Company’s previously filed Annual Report on Form 10-K for the year ended December 31, 2019 filed with the SEC on March 13, 2020. Refer to Note 3, “Research and Development Collaboration Agreements”, for more details about the Takeda Collaboration Agreement, the Takeda Multi-Target Agreement and the Takeda Development and License Agreement. Jonathan Lanfear, a director of the Company, was the Vice President and Global Head of Oncology and Neuroscience Business Development for Takeda until September 25, 2020.

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	NOTE 5 —MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS The following table sets forth the Company’s financial assets (cash equivalents and marketable securities) at fair value on a recurring basis (in thousands): Basis of Fair Value Measurements September 30, 2020 Level 1 Level 2 Level 3 Money market funds $ 27,080 $ 27,080 $ — $ — Commercial paper 43,911 — 43,911 — United States Treasury Bills 36,881 — 36,881 — United States government-related debt securities 6,021 — 6,021 — Corporate bonds 1,003 — 1,003 — Total $ 114,896 $ 27,080 $ 87,816 $ — Amounts included in: Cash and cash equivalents $ 30,080 Marketable securities, current 82,816 Marketable securities, non-current 2,000 Total cash equivalents and marketable securities $ 114,896 Basis of Fair Value Measurements December 31, 2019 Level 1 Level 2 Level 3 Money market funds $ 79,970 $ 79,970 $ — $ — Commercial paper 20,436 — 20,436 — United States Treasury Bills 16,738 — 16,738 — United States government-related debt securities 7,010 — 7,010 — Corporate bonds 1,351 — 1,351 — Total $ 125,505 $ 79,970 $ 45,535 $ — Amounts included in: Cash and cash equivalents $ 84,362 Marketable securities, current 39,633 Marketable securities, non-current 1,510 Total cash equivalents and marketable securities $ 125,505 The Company invests in highly-liquid, investment-grade securities. The following is a summary of the Company’s available-for-sale securities (in thousands): September 30, 2020 Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper and corporate bonds $ 30,080 $ — $ — $ 30,080 Marketable securities, current - commercial paper, Treasury bills and corporate bonds 82,743 75 (2 ) 82,816 Marketable securities, non-current - Treasury bills $ 2,000 $ — $ — $ 2,000 December 31, 2019 Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper and corporate bonds $ 84,361 $ 1 $ — $ 84,362 Marketable securities, current - commercial paper, Treasury bills and corporate bonds 39,616 17 — 39,633 Marketable securities, non-current - Treasury bills 1,510 — — 1,510 The following summarizes the contractual maturities of the Company’s available-for-sale investments: September 30, 2020 Cost Basis Fair Value Due in one year or less $ 112,823 $ 112,896 Due after one year through five years 2,000 2,000 Total $ 114,823 $ 114,896 December 31, 2019 Cost Basis Fair Value Due in one year or less $ 123,977 $ 123,995 Due after one year through five years 1,510 1,510 Total $ 125,487 $ 125,505 The Company received no proceeds and $1.3 million of proceeds from the sale of available-for-sale securities for the, nine months ended September 30, 2020 and September 30, 2019 respectively, with an immaterial realized gain for the nine months ended September 30, 2019. The basis on which the cost of the security sold was determined is specific identification.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	NOTE 6 — BALANCE SHEET COMPONENTS Accrued liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Accrued liabilities: General and administrative $ 1,648 $ 4,521 Clinical trial related costs 2,932 1,383 Non-clinical research and manufacturing operations 4,674 5,774 Payroll related 3,924 2,849 Other accrued expenses 53 17 Total Accrued liabilities $ 13,231 $ 14,544

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	NOTE 7—PROPERTY AND EQUIPMENT Property and equipment consisted of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory equipment $ 13,945 $ 10,587 Leasehold improvements 12,260 10,383 Furniture and fixtures 150 150 Computer and equipment 549 331 26,904 21,451 Less: Accumulated depreciation (6,015 ) (3,293 ) Total property and equipment, net $ 20,889 $ 18,158 Depreciation expense was $1.2 million and $0.5 million for the three months ended September 30, 2020 and September 30, 2019, respectively and $2.7 million and $1.3 million for the nine months ended September 30, 2020 and September 30, 2019, respectively. In connection with the continued expansion of the Company’s facilities, the Company had at September 30, 2020 and December 31, 2019, net ARO assets totaling $0.8 million and $1.0 million, respectively. The ARO assets are included in leasehold improvements.

Borrowing Arrangements

Borrowing Arrangements	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Borrowing Arrangements	NOTE 8 — BORROWING ARRANGEMENTS Perceptive Credit Facility On February 27, 2018, the Company entered into a term loan facility with Perceptive Credit Holdings II, LP (“Perceptive”) in the amount of $10.0 million (the “Perceptive Credit Facility”). The Perceptive Credit Facility consisted of a $5.0 million term loan, which was drawn on the effective date of the Perceptive Credit Facility, and an additional $5.0 million term loan which the Company did not draw down. The principal on the facility accrued interest at an annual rate equal to a three-month LIBOR plus the Applicable Margin. The Applicable Margin was 11.00%. Upon the occurrence, and during the continuance, of an event of default, the Applicable Margin, defined above, would be increased by 4.00% per annum. Payments for the first 24 months were interest only and paid quarterly. After the second anniversary of the closing date of the Perceptive Credit Facility, principal payments of $0.2 million were due each calendar quarter. The Company incurred $0.5 million in deferred finance costs and issued the debt net of a $1.5 million discount. The Company repaid the Perceptive Credit Facility on May 21, 2020, from the proceeds of the K2 Loan and Security Agreement In connection with the Perceptive Credit Facility, on February 27, 2018 the Company issued Perceptive a warrant to purchase 190,000 shares of the Company’s common stock. The warrant is exercisable for a period of seven years from the date of issuance at an exercise price per share of $9.5792, subject to certain adjustments as specified in the Warrant. For more information refer to Note 11, “Stockholders Equity” included in the Annual Report on Form 10-K for the year ended December 31, 2019 filed with the SEC on March 13, 2020. The fair value of the warrant of $1.5 million was recorded as a debt discount at issuance and was included in the loss on extinguishment. K2 Health Ventures Loan and Security Agreement On May 21, 2020, the Company entered into a Loan and Security Agreement with K2 HealthVentures LLC in the amount of $45.0 million (“K2 Loan and Security Agreement”). The K2 Loan and Security Agreement consists of three tranches, the first of which was drawn on the closing date in the amount of $15.0 million. The second tranche of $20.0 million may be drawn between March 1, 2021 and June 30, 2021 at the Company’s option and subject to the achievement of certain clinical milestones. A third tranche of $10.0 million may be drawn after the Company’s second tranche draw, but prior to December 31, 2021. The principal accrues interest at an annual rate equal to the greater of 8.45% or the sum of the Prime Rate plus 5.2% and commenced on July 1, 2020. The interest rate at September 30, 2020 was 8.45%. Payments are interest only until July 1, 2022, provided, however, that if no event of default has occurred and the second tranche has been fully funded payments will be interest only until July 1, 2023. After the second anniversary of the closing date of the K2 Loan and Security Agreement, principal payments are due monthly. The loan matures on June 1, 2024 and includes both financial and non-financial covenants . The Company expects to be compliant with the debt covenants for the next 12 months. The Company recorded the debt net of $1.1 million comprised of deferred financing costs, debt discount and associated exit fee which are being accreted to interest expense over the term of the K2 Loan and Security Agreement using the effective interest method. Additionally, the Company incurred $0.2 million in facilities fee related to the second tranche which will be classified as a prepaid asset until drawn upon. As of September 30, 2020 and December 31, 2019, the Perceptive Credit Facility principal balance was $0.0 million and $5.0 million, respectively. As of September 30, 2020 and December 31, 2019, the K2 Loan principal balance was $15.0 million and $0.0 million, respectively. As of September 30, 2020 and December 31, 2019, the carrying value of the long-term debt was $14.8 million and $3.7 million, respectively. Future required principal and final payments on the K2 Loan were as follows at September 30, 2020 ($ in thousands): 2020 — 2021 — 2022 3,507 2023 7,483 2024 4,010 Total Principal Amounts 15,000 Final Fee Due at Maturity 839 Unamortized discount, deferred costs and final fee (1,017 ) Total Long-Term Debt, net 14,822

Leases

Leases	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	NOTE 9 – LEASES On January 1, 2019, the Company adopted a new accounting standard that amends the guidance for the accounting and reporting of leases. Required disclosures have been made on a modified retrospective basis in accordance with the guidance of the standard. See Note 1, “Organization and Summary of Significant Accounting Policies” of the Company’s previously filed Annual Report on Form 10-K for the year ended December 31, 2019 filed with the SEC on March 13, 2020 for further discussion of the Company’s Lease accounting policy. The Company has operating leases for administrative offices and research and development facilities, and certain finance leases for equipment. The operating leases have remaining terms of less than two years to less than eight years, and the finance leases have remaining terms of less than one year. Leases with an initial term of 12 months or less will not be recorded on the condensed consolidated balance sheets as operating leases or finance leases, and the Company will recognize lease expense for these leases on a straight-line basis over the lease term. For leases commencing in 2019 and later, the Company will account for lease components (e.g., fixed payments including rent, real estate taxes, and insurance costs) with non-lease components (e.g. common area maintenance costs). Certain leases include options to renew, with renewal terms that can extend the lease term from three to five years. The exercise of lease renewal options for the Company’s existing leases is at its sole discretion and not included in the measurement of lease liability and ROU asset as they are not reasonably certain to be exercised. Certain finance leases also include options to purchase the leased equipment. The depreciable life of assets and leasehold improvements are limited by the expected lease term, unless there is a transfer of title or purchase option reasonably certain of exercise. The leases do not contain any residual value guarantees or material restrictive covenants. In January 2019, the Company entered into a lease agreement for an additional 57,000 square feet of administrative office and research and development space in Austin, Texas. The lease commenced March 2019 and expires August 2028 and does not contain an option to renew. The tables below include the impact of this lease. Upon the commencement of the lease, the Company recorded an operating lease ROU asset and a lease liability of $7.2 million. In connection with entering into the lease and in lieu of a cash deposit, the Company obtained a letter of credit of $3.0 million. Additionally, the Company has recorded an asset retirement obligation as a result of this lease which has a balance of $0.4 million at September 30, 2020. In June 2020, the Company entered into a lease agreement for office space in New York, New York. The space consists of an initial 9,289 square feet and an additional 3,000 square feet upon expansion. The lease for the initial space commenced on August 1, 2020. The expansion space will commence on the later of (i) the commencement date or (ii) the date on which there has been delivery of vacant possession. The possession of the expansion space shall not commence prior to November 1, 2020. The term for both spaces will expire on October 30, 2025 and does not contain an option to renew. In connection with entering into the lease and in lieu of a cash deposit, the Company obtained a letter of credit in the amount of $0.2 million. The components of lease expense were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2020 Operating leases Operating lease expense $ 671 $ 1,794 Variable lease expense 124 $ 369 Total operating lease expense $ 795 $ 2,163 Finance leases Amortization of right-of-use asset $ 2 $ 6 Interest on lease liabilities - - Total finance lease expense $ 2 $ 6 The following table summarizes the balance sheet classification of leases at September 30, 2020(in thousands): Operating leases Operating lease right-of-use assets, non-current $ 11,589 Operating lease liabilities, current 1 $ 2,038 Operating lease liabilities, non-current 12,828 Total operating lease liabilities $ 14,866 Finance leases Property and equipment, at cost $ 77 Less, Accumulated depreciation 47 Property and equipment, net $ 30 Finance lease liabilities, current 1 $ 3 1. Included in other current liabilities. The following table presents other information on leases as of September 30, 2020: Weighted Average Remaining Lease Term Weighted Average Discount Rate Operating leases 6.3 7.03 % Finance leases 0.3 6.51 % Maturities of lease liabilities were as follows as of September 30, 2020 (in thousands): Operating Leases Finance Leases 2020, remainder $ 683 $ 3 2021 3,155 2022 3,361 2023 2,689 2024 2,218 2025 2,147 Thereafter 4,246 Total lease payments 18,499 3 Less: Imputed interest (3,633 ) — Total lease liabilities $ 14,866 $ 3 Supplemental cash flow information related to the Company’s leases were as follows for the nine months ended September 30, 2020 (in thousands): Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 1,771 Operating cash flows from finance leases $ 1 Financing cash flows from finance leases $ 16

Contractual Commitments

Contractual Commitments	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Contractual Commitments	NOTE 10 — CONTRACTUAL COMMITMENTS The Company has entered into project work orders for each of its clinical trials with clinical research organizations (each being a “CRO”) and related laboratory vendors. Under the terms of these agreements, the Company is required to pay certain upfront fees for direct services costs. Based on the particular agreement some of the fees may be for services yet to be rendered and are reflected as a current prepaid asset and have an unamortized balance of approximately $1.3 million at September 30, 2020. In connection with the Company’s clinical trials, the Company has entered into separate project work orders for each trial with its CRO. The Company has entered into agreements with CROs and other external service providers for services, primarily in connection with the clinical trials and development of the Company’s drug or biologic candidates. The Company was contractually obligated for up to approximately $16.4 million of future services under these agreements at September 30, 2020, for which amounts have not been accrued as services have not been performed. The Company’s actual contractual obligations will vary depending upon several factors, including the progress and results of the underlying services. The Company has entered into estimated purchase obligations which in total range from $11.2 million to $12.1 million and include signed orders for capital equipment. As a result of the Takeda Development and License Agreement, the Company exercised its right to cost-share approximately 50% of the development costs for Phase I. Future clinical trial expense related to this trial has not been included within the purchase commitments because they are contingent on enrollment in clinical trials and the activities required to be performed by the clinical sites.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	NOTE 11 — STOCK-BASED COMPENSATION Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 1,774 $ 655 $ 4,636 $ 1,690 General and administrative 1,511 872 3,891 2,640 Total stock-based compensation $ 3,285 $ 1,527 $ 8,527 $ 4,330 At September 30, 2020, the total unrecognized compensation cost related to unvested stock-based awards granted to employees under the Company’s equity incentive plans was approximately $33.9 million. This cost will be recorded as compensation expense on a ratable basis over the remaining weighted average requisite service period of approximately 2.7 years. Valuation Assumptions The Company estimated the fair value of stock options granted using the Black-Scholes option-pricing formula and a single option award approach. This fair value is being amortized ratably over the requisite service periods of the awards, which is generally the vesting period. The fair value of employee stock options was estimated using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Employee Stock Options: Risk-free interest rate 0.49 % 1.87 % 1.47 % 2.47 % Expected term (in years) 6.08 6.08 6.08 6.08 Dividend yield — — — — Volatility 112.02 % 107.21 % 110.81 % 108.67 % Weighted-average fair value of stock options granted $ 9.29 $ 4.96 $ 11.89 $ 4.36 Equity Incentive Plans These plans consist of the 2018 Equity Incentive Plan; the 2014 Equity Incentive Plan, as amended; the 2004 Amended and Restated Equity Incentive Plan; and the Amended and Restated 2004 Employee Stock Purchase Plan. As of May 31, 2018, the 2014 Equity Incentive Plan; and the 2004 Equity Incentive Plan were terminated, and no further shares will be granted from those plans. The following table summarizes stock option activity under the Company’s equity incentive plans: Options Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (in millions) Outstanding at December 31, 2019 4,763,062 $ 6.36 8.1 $ 36.6 Granted 2,374,006 $ 14.23 — $ — Exercised (240,659 ) $ 3.87 — $ — Forfeitures (104,436 ) $ 11.12 — $ — Outstanding at September 30, 2020 6,791,973 $ 9.12 8.2 $ 20.5 Exercisable at September 30, 2020 2,554,485 $ 6.47 7.1 $ 11.9 The total intrinsic value of stock options exercised during the nine months ended September 30, 2020 and September 30, 2019 was $2.4 million and $0.3 million, respectively, as determined at the date of the option exercise. Cash received from stock option exercises was $0.9 million and $1.3 million for the nine months ended September 30, 2020 and 2019, respectively. The Company issues new shares of common stock upon exercise of options. In connection with these exercises, there was no tax benefit realized by the Company due to the Company’s current loss position.

In-Process Research and Develop

In-Process Research and Development	9 Months Ended
	Sep. 30, 2020
Research And Development [Abstract]
In-Process Research and Development	NOTE 12 – IN-PROCESS RESEARCH AND DEVELOPMENT In-process research and development represent the fair value of the Company’s legacy program, Evofosfamide, which was acquired as a part of the merger agreement with Threshold. For more information regarding the merger refer to Note 1, “Organization and Summary of Significant Accounting Policies ” . Fair value of in-process research and development is estimated based upon internal evaluation of each asset that includes quantitative analyses of net revenue and cash flows, review of recent sales of similar assets and market responses based upon discussions in connection with offers received from potential buyers. Certain factors used for these types of nonrecurring fair value measurements are considered Level 3 inputs. The Company obtained a fair value estimate, from a third party specialist as of August 1, 2019, and determined the asset was impaired and the value was not fully recoverable. During the year ended December 31, 2019, the Company recorded a related impairment of $22.1 million. Future write-downs of the asset are possible based upon the amount of proceeds from an eventual sale of the asset. Additionally, the Company classifies the remaining $4.5 million - held for sale as the Company plans to sell the asset within the next year

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Stockholders' Equity	NOTE 13 – STOCKHOLDERS’ EQUITY In July 2020, the Company raised gross proceeds of approximately $50.0 million and net proceeds of $48.5 million through at-the-market sales (“ATM”) of its common stock pursuant to its ATM facility. The Company sold approximately 3.6 million shares of the Company’s common stock at a purchase price of $12.00 per share and 0.5 million shares at a purchase price of $12.70, in each case the market price at the time of sale. These sales constituted the full available dollar amount under the Company’s current ATM facility, and with such completion, its current ATM facility has terminated. On August 7, 2020, the Company filed with the Securities and Exchange Commission (“SEC”) a registration statement on Form S-3 for $300.0 million of securities (the “Shelf Registration Statement”), inclusive of a $100.0 million ATM program. This Shelf Registration Statement is in replacement of the Company’s existing registration statement on Form S-3 and incorporates the unsold balance remaining thereto. The SEC declared the Shelf Registration Statement effective on August 17, 2020 and the Company may make sales of securities from time to time, depending on market conditions, pursuant to the Shelf Registration Statement.

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America and include the accounts of the Company and its wholly owned subsidiary, and reflect the elimination of intercompany accounts and transactions. The preparation of condensed consolidated financial statements requires management to make estimates and assumptions that affect the recorded amounts reported therein. The business and economic uncertainty resulting from the COVID-19 pandemic has made such estimates and assumptions more difficult to calculate. Accordingly, actual results and outcomes could differ from those estimates, and a change in facts or circumstances surrounding the estimates could result in a change to estimates and impact future operating results. The unaudited condensed consolidated financial statements and related disclosures have been prepared with the presumption that users of the interim unaudited condensed consolidated financial statements have read or have access to the audited consolidated financial statements for the preceding fiscal year. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 13, 2020.
Reclassifications	Reclassifications Certain amounts in the prior year’s presentation have been reclassified to conform to the current presentation. The condensed consolidated balance sheet at December 31, 2019 included herein was derived from the audited financial statements at that date, but includes a reclassification of $8.8 million from Deferred revenue, current to Deferred revenue, current, related party and $0.4 million from Deferred revenue, non-current to Deferred revenue, non-current, related party in order to conform to current period presentation. The condensed consolidated statements of cash flow for the nine months ended September 30, 2019, included herein includes a reclassification of $12.7 million from Deferred revenue to Deferred revenue, related party.
Liquidity	Liquidity At September 30, 2020, we had cash, cash equivalents, and marketable securities of $118.2 million. The Company has devoted substantially all of its resources to developing its ETB candidates and platform technology, building its intellectual property portfolio, developing its supply chain, conducting business planning, raising capital and providing for general and administrative support for these operations. The Company expects that its existing cash, cash equivalents and marketable securities will enable it to fund its operating expenses and capital expenditure requirements into the second half of 2022.
Significant Accounting Policies	Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2020, as compared to the significant accounting policies disclosed in Note 1, Summary of significant accounting policies, to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers temporary investments having original maturities of three months or less from date of purchase to be cash equivalents. Restricted cash is recorded in other assets, based on when the restrictions expire. Other assets includes $3.7 million of restricted cash at September 30, 2020 and $3.0 million at December 31, 2019.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash and cash equivalents are with two major financial institutions in the United States. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. The Company’s exposure to credit risk associated with non-payment will be affected principally by conditions or occurrences within Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda Pharmaceutical Company Ltd. (“Takeda”) and Vertex Pharmaceuticals Incorporated (“Vertex”) In July 2020, the Company became aware of one potentially non-conforming batch of a single Company product fill, which may not meet manufacturing specifications. The Company continues to investigate the batch. The Company continues to investigate the batch. If upon the conclusion of the batch evaluation such batch is deemed to be non-conforming this could result in a reversal of revenue in future periods as the Company recognizes collaboration revenue over time by measuring toward completion to satisfy the performance obligation. The Company does not believe this potential non-conforming batch will result in an increased timeline for its ongoing projects nor does it affect any other batches, production, or manufacturing. The Company expects to be able to meet the supply needs for all of its active clinical trials. Drug or biologic candidates developed by the Company may require approvals or clearances from the U.S. Food and Drug Administration (“FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug or biologic candidates will receive any of the required approvals or clearances. If the Company were to be denied approval or clearance or any such approval or clearance were to be delayed, it would have a material adverse impact on the Company.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (“ In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). ASU 2018-15 aligns the accounting for implementation costs incurred in a hosting arrangement that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. This ASU was effective for annual periods beginning after December 15, 2019, including interim periods within that period, and early adoption is permitted. The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606, which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC Topic 606 when the counterparty is a customer. In addition, Topic 808 precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance was effective for the Company beginning January 1, 2020 . The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses, which requires recognizing credit losses on financial instruments based on an estimate of current expected credit losses. The new guidance applies to loans, accounts receivable, trade receivables, other financial assets measured at amortized cost, loan commitments and other off-balance sheet credit exposures. The new guidance also applies to debt securities and other financial assets measured at fair value through other comprehensive income. This guidance was effective for the Company beginning January 1, 2020 . The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740: Simplifying the Accounting for Income Taxes), which removes certain exceptions to the general principles in Topic 740. ASU 2019-12 is effective for the fiscal years beginning after December 15, 2020, with early adoption permitted. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848: Facilitation of the Effects of Reference Rate Reform on Financial Reporting). The new guidance provides optional guidance for a limited period of time for applying U.S. GAAP to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. The guidance will be effective prospectively as of March 12, 2020 through December 31, 2022 and interim periods within those fiscal years. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. In August 2020, the FASB issued ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (Subtopic 470-20: Debt with Conversion and Other Options and Subtopic 815-40: Derivatives and Hedging— Contracts in Entity’s Own Equity). The new guidance simplifies accounting for convertible instruments by removing major separation models, removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception and it also simplifies the diluted earnings per share calculation in certain areas. The amendment is effective for the Company for fiscal years beginning after December 15, 2023. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Research and Development Agre_2

Research and Development Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Schedule of Research and Development Revenues Disaggregated by Location	Research and development revenue is attributable to regions based on the location of the Company’s collaboration partner's parent company headquarters. Research and development revenues disaggregated by location were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Japan $ 1,566 $ 2,903 $ 4,962 $ 14,527 United States 2,732 284 7,176 284 Total research and development revenue $ 4,298 $ 3,187 $ 12,138 $ 14,811
Millennium Pharmaceuticals Inc
Schedule of Research and Development Revenue from Related Party Relates to Revenue from Research and Development Agreements	Research and development revenue from related party relates to revenue from research and development agreements with Millennium Pharmaceuticals, Inc., a wholly-owned subsidiary of Takeda and were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Takeda Individual Project Agreement $ — $ — $ — $ 54 Takeda Development and License Agreement 86 2,581 307 13,707 Takeda Multi-Target Agreement 1,480 322 4,655 766 Total research and development revenue, related party $ 1,566 $ 2,903 $ 4,962 $ 14,527
Takeda
Schedule of Deferred Revenue, Other Liabilities for Co-share Payments and Accounts Receivable Balances from Research and Development Agreements	At September 30, 2020 and December 31, 2019, the Company had deferred revenue, other liabilities for co-share payments and accounts receivable balances from the research and development agreements with Takeda, who is a related party. These amounts were as follows (in thousands): September 30, 2020 December 31, 2019 Assets Accounts receivable $ 301 $ 408 Liabilities Other current liabilities $ 5,498 — Deferred revenue, current 4,566 8,780 Deferred revenue, non-current 935 441 Other liabilities 6,711 — Total liabilities $ 17,710 $ 9,221

Marketable Securities and Fai_2

Marketable Securities and Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Financial Assets at Fair Value on Recurring Basis	The following table sets forth the Company’s financial assets (cash equivalents and marketable securities) at fair value on a recurring basis (in thousands): Basis of Fair Value Measurements September 30, 2020 Level 1 Level 2 Level 3 Money market funds $ 27,080 $ 27,080 $ — $ — Commercial paper 43,911 — 43,911 — United States Treasury Bills 36,881 — 36,881 — United States government-related debt securities 6,021 — 6,021 — Corporate bonds 1,003 — 1,003 — Total $ 114,896 $ 27,080 $ 87,816 $ — Amounts included in: Cash and cash equivalents $ 30,080 Marketable securities, current 82,816 Marketable securities, non-current 2,000 Total cash equivalents and marketable securities $ 114,896 Basis of Fair Value Measurements December 31, 2019 Level 1 Level 2 Level 3 Money market funds $ 79,970 $ 79,970 $ — $ — Commercial paper 20,436 — 20,436 — United States Treasury Bills 16,738 — 16,738 — United States government-related debt securities 7,010 — 7,010 — Corporate bonds 1,351 — 1,351 — Total $ 125,505 $ 79,970 $ 45,535 $ — Amounts included in: Cash and cash equivalents $ 84,362 Marketable securities, current 39,633 Marketable securities, non-current 1,510 Total cash equivalents and marketable securities $ 125,505
Summary of Company's Available-for-Sale Securities	The Company invests in highly-liquid, investment-grade securities. The following is a summary of the Company’s available-for-sale securities (in thousands): September 30, 2020 Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper and corporate bonds $ 30,080 $ — $ — $ 30,080 Marketable securities, current - commercial paper, Treasury bills and corporate bonds 82,743 75 (2 ) 82,816 Marketable securities, non-current - Treasury bills $ 2,000 $ — $ — $ 2,000 December 31, 2019 Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper and corporate bonds $ 84,361 $ 1 $ — $ 84,362 Marketable securities, current - commercial paper, Treasury bills and corporate bonds 39,616 17 — 39,633 Marketable securities, non-current - Treasury bills 1,510 — — 1,510
Summary of Contractual Maturities of Available-for-Sale-Investment	The following summarizes the contractual maturities of the Company’s available-for-sale investments: September 30, 2020 Cost Basis Fair Value Due in one year or less $ 112,823 $ 112,896 Due after one year through five years 2,000 2,000 Total $ 114,823 $ 114,896 December 31, 2019 Cost Basis Fair Value Due in one year or less $ 123,977 $ 123,995 Due after one year through five years 1,510 1,510 Total $ 125,487 $ 125,505

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Components of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): September 30, 2020 December 31, 2019 Accrued liabilities: General and administrative $ 1,648 $ 4,521 Clinical trial related costs 2,932 1,383 Non-clinical research and manufacturing operations 4,674 5,774 Payroll related 3,924 2,849 Other accrued expenses 53 17 Total Accrued liabilities $ 13,231 $ 14,544

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment consisted of the following (in thousands): September 30, 2020 December 31, 2019 Laboratory equipment $ 13,945 $ 10,587 Leasehold improvements 12,260 10,383 Furniture and fixtures 150 150 Computer and equipment 549 331 26,904 21,451 Less: Accumulated depreciation (6,015 ) (3,293 ) Total property and equipment, net $ 20,889 $ 18,158

Borrowing Arrangements (Tables)

Borrowing Arrangements (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Required Future Principal Payments	Future required principal and final payments on the K2 Loan were as follows at September 30, 2020 ($ in thousands): 2020 — 2021 — 2022 3,507 2023 7,483 2024 4,010 Total Principal Amounts 15,000 Final Fee Due at Maturity 839 Unamortized discount, deferred costs and final fee (1,017 ) Total Long-Term Debt, net 14,822

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Components of Lease Expense	The components of lease expense were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2020 Operating leases Operating lease expense $ 671 $ 1,794 Variable lease expense 124 $ 369 Total operating lease expense $ 795 $ 2,163 Finance leases Amortization of right-of-use asset $ 2 $ 6 Interest on lease liabilities - - Total finance lease expense $ 2 $ 6
Schedule of Balance Sheets Classification of Leases	The following table summarizes the balance sheet classification of leases at September 30, 2020(in thousands): Operating leases Operating lease right-of-use assets, non-current $ 11,589 Operating lease liabilities, current 1 $ 2,038 Operating lease liabilities, non-current 12,828 Total operating lease liabilities $ 14,866 Finance leases Property and equipment, at cost $ 77 Less, Accumulated depreciation 47 Property and equipment, net $ 30 Finance lease liabilities, current 1 $ 3 1. Included in other current liabilities.
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities were as follows as of September 30, 2020 (in thousands): Operating Leases Finance Leases 2020, remainder $ 683 $ 3 2021 3,155 2022 3,361 2023 2,689 2024 2,218 2025 2,147 Thereafter 4,246 Total lease payments 18,499 3 Less: Imputed interest (3,633 ) — Total lease liabilities $ 14,866 $ 3
Supplemental Cash Flow Information	Supplemental cash flow information related to the Company’s leases were as follows for the nine months ended September 30, 2020 (in thousands): Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 1,771 Operating cash flows from finance leases $ 1 Financing cash flows from finance leases $ 16

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation Expense	Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 1,774 $ 655 $ 4,636 $ 1,690 General and administrative 1,511 872 3,891 2,640 Total stock-based compensation $ 3,285 $ 1,527 $ 8,527 $ 4,330
Weighted-Average Fair Value Valuation Assumptions	The fair value of employee stock options was estimated using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Employee Stock Options: Risk-free interest rate 0.49 % 1.87 % 1.47 % 2.47 % Expected term (in years) 6.08 6.08 6.08 6.08 Dividend yield — — — — Volatility 112.02 % 107.21 % 110.81 % 108.67 % Weighted-average fair value of stock options granted $ 9.29 $ 4.96 $ 11.89 $ 4.36
Stock Option Activity Under Equity Incentive Plan	The following table summarizes stock option activity under the Company’s equity incentive plans: Options Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term Aggregate Intrinsic Value (in millions) Outstanding at December 31, 2019 4,763,062 $ 6.36 8.1 $ 36.6 Granted 2,374,006 $ 14.23 — $ — Exercised (240,659 ) $ 3.87 — $ — Forfeitures (104,436 ) $ 11.12 — $ — Outstanding at September 30, 2020 6,791,973 $ 9.12 8.2 $ 20.5 Exercisable at September 30, 2020 2,554,485 $ 6.47 7.1 $ 11.9

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Organization And Summary Of Significant Accounting Policies [Line Items]
Reclassification from deferred revenue, current to deferred revenue, current, related party	$ 4,566		$ 4,566		$ 8,780
Reclassification from deferred revenue, non-current to deferred revenue, non-current, related party					400
Reclassification from deferred revenue to deferred revenue, related party				$ 12,700
Cash, cash equivalents, and marketable securities	$ 118,200		$ 118,200
Revenue | Credit Risk | Vertex Pharmaceuticals Inc
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenues	64.00%	0.00%	47.00%	0.00%
Revenue | Credit Risk | Takeda
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenues	36.00%	80.00%	32.00%	90.00%
Other Assets
Organization And Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 3,700		$ 3,700		$ 3,000

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Detail) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Stock Options, Warrants and Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common shares excluded from the computation of diluted net loss per share on effect of anti-dilutive	9,996,000	8,121,000

Research and Development Agre_3

Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition [Line Items]
Total research and development revenue	$ 4,298	$ 3,187	$ 12,138	$ 14,811
JAPAN
Revenue Recognition [Line Items]
Total research and development revenue	1,566	2,903	4,962	14,527
UNITED STATES
Revenue Recognition [Line Items]
Total research and development revenue	$ 2,732	$ 284	$ 7,176	$ 284

Research and Development Agre_4

Research and Development Agreements - Schedule of Research and Development Revenue from Related Party Relates to Revenue from Research and Development Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition [Line Items]
Total research and development revenue, related party	$ 4,298	$ 3,187	$ 12,138	$ 14,811
Millennium Pharmaceuticals Inc
Revenue Recognition [Line Items]
Total research and development revenue, related party	1,566	2,903	4,962	14,527
Millennium Pharmaceuticals Inc | Takeda Individual Project Agreement
Revenue Recognition [Line Items]
Total research and development revenue, related party	0	0	0	54
Millennium Pharmaceuticals Inc | Takeda Development Agreement
Revenue Recognition [Line Items]
Total research and development revenue, related party	86	2,581	307	13,707
Millennium Pharmaceuticals Inc | Takeda Multi Target Agreement
Revenue Recognition [Line Items]
Total research and development revenue, related party	$ 1,480	$ 322	$ 4,655	$ 766

Research and Development Agre_5

Research and Development Agreements - Schedule of Deferred Revenue, Other Liabilities for Co-share Payments and Accounts Receivable Balances from the Research and Development Agreements (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Accounts receivable	$ 301	$ 408
Liabilities
Other current liabilities	2,041	2,501
Other liabilities	1,458	1,366
Total liabilities	84,936	71,174
Takeda
Assets
Accounts receivable	301	408
Liabilities
Other current liabilities	5,498	0
Deferred revenue, current	4,566	8,780
Deferred revenue, non-current	935	441
Other liabilities	6,711	0
Total liabilities	$ 17,710	$ 9,221

Research and Development Agre_6

Research and Development Agreements - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended			9 Months Ended		107 Months Ended
	Nov. 30, 2019	Jul. 31, 2019	Sep. 30, 2018	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Nov. 30, 2019	Dec. 31, 2019
Research And Development Collaboration Agreements [Line Items]
Common stock, shares issued				49,963,732			49,963,732			45,589,157
Common stock, par value				$ 0.001			$ 0.001			$ 0.001
Revenue from grant				$ 4,298,000		$ 3,618,000	$ 15,348,000	$ 16,073,000
Grant
Research And Development Collaboration Agreements [Line Items]
Revenue from grant				0		$ 431,000	3,210,000	$ 1,262,000
CPRIT Agreement | Cancer Prevention and Research Institute of Texas
Research And Development Collaboration Agreements [Line Items]
Product development grant awarded			$ 15,200,000
CPRIT Agreement | Cancer Prevention and Research Institute of Texas | ETB MT-3724
Research And Development Collaboration Agreements [Line Items]
Aggregate proceeds received from award granted									$ 10,600,000
Revenue from grant							16,400,000
Grants Receivable				3,500,000			3,500,000
Grant Agreements | Grants Revenue Receivable
Research And Development Collaboration Agreements [Line Items]
Reimbursement amounts submitted in excess of amounts received are recorded as receivables				3,500,000			3,500,000			$ 7,100,000
Takeda Development Agreement
Research And Development Collaboration Agreements [Line Items]
Total transaction price							29,800,000
Upfront payment					$ 30,000,000
Development milestone payment that is achievable							10,000,000
Expected co-share payments payable				10,200,000			10,200,000
Deferred revenue				2,700,000			2,700,000			6,100,000
Takeda Development Agreement | Clinical Development and Regulatory Milestones
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised		$ 307,500,000
Takeda Development Agreement | Sales Milestone
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised		$ 325,000,000
Takeda Multi Target Agreement | Takeda
Research And Development Collaboration Agreements [Line Items]
Deferred revenue				2,800,000			2,800,000			3,100,000
Cumulative payments received							5,000,000
Aggregate milestone payments upon exercise of option to license ETBS				30,000,000			30,000,000
Additional preclinical, clinical development and commercialization milestone payment				397,000,000			397,000,000
Takeda Multi Target Agreement | Takeda | Maximum
Research And Development Collaboration Agreements [Line Items]
Contractual contingency fees							10,000,000
Commercial milestone payment							150,000,000
Vertex Collaboration Agreement
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised	$ 180,000,000
Upfront payment	38,000,000
Deferred revenue				$ 20,300,000			$ 20,300,000			$ 27,500,000
Upfront payment, cash	23,000,000
Upfront payment, equity method investments	$ 15,000,000								$ 15,000,000
Common stock, shares issued	1,666,666								1,666,666
Common stock, par value	$ 0.001								$ 0.001
Vertex Collaboration Agreement | Common Stock
Research And Development Collaboration Agreements [Line Items]
Purchase price per share	$ 9								$ 9
Fair value of allocated consideration	$ 4,500,000
Vertex Collaboration Agreement | ETBs
Research And Development Collaboration Agreements [Line Items]
Aggregate milestone payments upon exercise of option to license ETBS	22,000,000								$ 22,000,000
Vertex Collaboration Agreement | Sales Milestone
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised	$ 70,000,000

Marketable Securities and Fai_3

Marketable Securities and Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 114,896	$ 125,505
Cash and cash equivalents	33,410	85,451	$ 15,268
Marketable securities, current	82,816	39,633
Marketable securities, non-current	2,000	1,510
Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	30,080	84,362
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	27,080	79,970
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	43,911	20,436
United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	36,881	16,738
United States Government-Related Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	6,021	7,010
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	1,003	1,351
Basis of Fair Value Measurements, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	27,080	79,970
Basis of Fair Value Measurements, Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	27,080	79,970
Basis of Fair Value Measurements, Level 1 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 1 | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 1 | United States Government-Related Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 1 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	87,816	45,535
Basis of Fair Value Measurements, Level 2 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	43,911	20,436
Basis of Fair Value Measurements, Level 2 | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	36,881	16,738
Basis of Fair Value Measurements, Level 2 | United States Government-Related Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	6,021	7,010
Basis of Fair Value Measurements, Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	1,003	1,351
Basis of Fair Value Measurements, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 3 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 3 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 3 | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 3 | United States Government-Related Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Basis of Fair Value Measurements, Level 3 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 0	$ 0

Marketable Securities and Fai_4

Marketable Securities and Fair Value Measurements - Summary of Company's Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	$ 114,823	$ 125,487
Fair Value	82,816	39,633
Fair Value	2,000	1,510
Cash Equivalents - Money Market Funds, Commercial Paper and Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	30,080	84,361
Unrealized Gain	0	1
Unrealized Loss	0	0
Fair Value	30,080	84,362
Marketable Securities, Current - Commercial Paper, Treasury Bills and Corporate Bonds
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	82,743	39,616
Unrealized Gain	75	17
Unrealized Loss	(2)	0
Fair Value	82,816	39,633
Marketable Securities, Non-current - Treasury Bills
Schedule Of Available For Sale Securities [Line Items]
Unrealized Gain	0	0
Unrealized Loss	0	0
Cost Basis	2,000	1,510
Fair Value	$ 2,000	$ 1,510

Marketable Securities and Fai_5

Marketable Securities and Fair Value Measurements - Summary of Contractual Maturities of Available-for-Sale-Investment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Cost Basis, Due in one year or less	$ 112,823	$ 123,977
Cost Basis, Due after one year through five years	2,000	1,510
Cost Basis	114,823	125,487
Fair Value, Due in one year or less	112,896	123,995
Fair Value, Due after one year through five years	2,000	1,510
Fair Value, Total	$ 114,896	$ 125,505

Marketable Securities and Fai_6

Marketable Securities and Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Proceeds from sale of available-for-sale securities	$ 0	$ 1,300,000

Balance Sheet Components - Comp

Balance Sheet Components - Components of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued Liabilities Current [Abstract]
General and administrative	$ 1,648	$ 4,521
Clinical trial related costs	2,932	1,383
Non-clinical research and manufacturing operations	4,674	5,774
Payroll related	3,924	2,849
Other accrued expenses	53	17
Total Accrued liabilities	$ 13,231	$ 14,544

Property and Equipment - Compon

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 26,904	$ 21,451
Less: Accumulated depreciation	(6,015)	(3,293)
Total property and equipment, net	20,889	18,158
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	13,945	10,587
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, Gross	12,260	10,383
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, Gross	150	150
Computer and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 549	$ 331

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Depreciation expense	$ 1.2	$ 0.5	$ 2.7	$ 1.3
Leasehold Improvements
Property Plant And Equipment [Line Items]
Asset retirement obligation, asset	$ 0.8		$ 0.8		$ 1

Borrowing Arrangements - Additi

Borrowing Arrangements - Additional Information (Detail) - USD ($)	May 21, 2020	Feb. 27, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 0	$ 0	$ (1,237,000)	$ 0
Long-term debt, carrying value			$ 14,800,000		$ 14,800,000		$ 3,700,000
K2 Loan and Security Agreement
Debt Instrument [Line Items]
Loan and security agreement	$ 45,000
Interest rate			8.45%		8.45%
Debt net			$ 1,100		$ 1,100
Total debt			$ 15,000,000		$ 15,000,000		0
Tranche One | K2 Loan and Security Agreement
Debt Instrument [Line Items]
Loan and security agreement	15,000
Tranche Two | K2 Loan and Security Agreement
Debt Instrument [Line Items]
Loan and security agreement	20,000
Interest rate			0.20%		0.20%
Tranche Three | K2 Loan and Security Agreement
Debt Instrument [Line Items]
Loan and security agreement	$ 10,000
Prime Rate | K2 Loan and Security Agreement
Debt Instrument [Line Items]
Interest rate			5.20%		5.20%
Perceptive
Debt Instrument [Line Items]
Credit Facility, principal payments					$ 4,900,000
Credit Facility, interest expense					4,900,000
Exit fees and prepayment penalties			$ 100,000		100,000
Loss on extinguishment of debt					(1,200,000)
Total debt			0		$ 0		$ 5,000,000
Term Loan Facility | Perceptive
Debt Instrument [Line Items]
Maximum borrowing capacity under loan		$ 10,000,000
Increase in applicable margin percentage on event of default		4.00%
Period for which interest only payments will be made		24 months
Credit Facility, principal payments			$ 200,000
Deferred finance costs		$ 500,000
Debt issuance cost, net of discount		$ 1,500,000
Number of shares issued for each warrant		190,000
Warrant exercisable period		7 years
Warrant exercise price		$ 9.5792
Fair value of the warrant recorded as a debt discount		$ 1,500,000
Term Loan Facility | Perceptive | LIBOR
Debt Instrument [Line Items]
Applicable margin percentage		11.00%
Term Loan Facility | Perceptive | Term Loan Drawn on Effective Date of Credit Facility
Debt Instrument [Line Items]
Proceeds from initial term loan on closing date of Credit Facility		$ 5,000,000
Term Loan Facility | Perceptive | Additional Term Loan Drawn Six Months Following Effective Date of Credit Facility
Debt Instrument [Line Items]
Remaining available amount from credit facility did not draw down		$ 5,000,000

Borrowing Arrangements - Schedu

Borrowing Arrangements - Schedule of Required Future Principal Payments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total Long-Term Debt, net	$ 14,800	$ 3,700
K2 Loan and Security Agreement
Debt Instrument [Line Items]
2020	0
2021	0
2022	3,507
2023	7,483
2024	4,010
Total Principal Amounts	15,000
Final Fee Due at Maturity	839
Unamortized discount, deferred costs and final fee	(1,017)
Total Long-Term Debt, net	$ 14,822

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended		9 Months Ended
	Jun. 30, 2020USD ($)ft²	Jan. 31, 2019USD ($)ft²	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use-asset			$ 11,589	$ 9,959
Operating lease, lease liability			14,866
Texas
Lessee Lease Description [Line Items]
Area of administrative office and research and development space leased | ft²		57,000
Lease expiration period		2028-08
Operating lease right-of-use-asset		$ 7,200
Operating lease, lease liability		7,200
Asset retirement obligation, lease			$ 400
Texas | Letter of Credit
Lessee Lease Description [Line Items]
Letter of credit		$ 3,000
New York
Lessee Lease Description [Line Items]
Area of land | ft²	9,289
Area of land of additional facility lease agreement | ft²	3,000
Lease expiration date	Oct. 30, 2025
New York | Letter of Credit
Lessee Lease Description [Line Items]
Letter of credit	$ 200
Minimum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term.			2 years
Lessee, finance leases remaining lease term.			1 year
Lessee, operating leases renewal lease term			3 years
Maximum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term.			8 years
Lessee, operating leases renewal lease term			5 years

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Leases [Abstract]
Operating lease expense	$ 671	$ 1,794
Variable lease expense	124	369
Total operating lease expense	795	2,163
Amortization of right-of-use asset	2	6
Interest on lease liabilities	0	0
Total finance lease expense	$ 2	$ 6

Leases - Schedule of Balance Sh

Leases - Schedule of Balance Sheets Classification of Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Operating leases
Operating lease right-of-use assets, non-current	$ 11,589	$ 9,959
Operating lease liabilities, current	2,038
Operating lease liabilities, non-current	12,828	$ 11,682
Total operating lease liabilities	14,866
Finance leases
Property and equipment, at cost	77
Less, Accumulated depreciation	47
Property and equipment, net	$ 30
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet
Finance lease liabilities, current	$ 3
Finance Lease Liability Current Statement Of Financial Position Extensible List	us-gaap:OtherLiabilitiesCurrent

Leases - Schedule of Leases Inf

Leases - Schedule of Leases Information (Detail)	Sep. 30, 2020
Weighted average discount rate
Operating leases	7.03%
Finance leases	6.51%
Weighted average remaining lease term
Operating leases	6 years 3 months 18 days
Finance leases	3 months 18 days

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Sep. 30, 2020USD ($)
Lease payments
2020, remainder	$ 683
2021	3,155
2022	3,361
2023	2,689
2024	2,218
2025	2,147
Thereafter	4,246
Total lease payments	18,499
Less: Imputed interest	(3,633)
Total lease liabilities	14,866
Finance Leases
2020, remainder	3
2021	0
2022	0
2023	0
2024	0
2025	0
Thereafter	0
Total lease payments	3
Less: Imputed interest	0
Total lease liabilities	$ 3

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 1,771
Operating cash flows from finance leases	1
Financing cash flows from finance leases	$ 16

Contractual Commitments - Addit

Contractual Commitments - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Other Commitments [Line Items]
Upfront fees unamortized balance included in prepaid asset	$ 1.3
Contractual obligation	$ 16.4
Percentage of right to share development costs exercised	50.00%
Minimum
Other Commitments [Line Items]
Estimated purchase obligation	$ 11.2
Maximum
Other Commitments [Line Items]
Estimated purchase obligation	$ 12.1

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 3,285	$ 1,527	$ 8,527	$ 4,330
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	1,774	655	4,636	1,690
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,511	$ 872	$ 3,891	$ 2,640

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans	$ 33,900,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans, period for recognition	2 years 8 months 12 days
Total intrinsic value of stock options exercised	$ 2,400,000	$ 300,000
Cash received from stock option exercises	930,000	1,300,000
Tax benefit realized upon exercise of option	$ 0	$ 0

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.49%	1.87%	1.47%	2.47%
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days	6 years 29 days
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility	112.02%	107.21%	110.81%	108.67%
Weighted-average fair value of stock options granted	$ 9.29	$ 4.96	$ 11.89	$ 4.36

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Outstanding, Beginning Balance	4,763,062
Number of Shares, Granted	2,374,006
Number of Shares, Exercised	(240,659)
Number of Shares, Forfeitures	(104,436)
Number of Shares, Outstanding, Ending Balance	6,791,973	4,763,062
Number of Shares, Exercisable	2,554,485
Weighted-Average Exercise Price, Outstanding, Beginning Balance	$ 6.36
Weighted-Average Exercise Price, Granted	14.23
Weighted-Average Exercise Price, Exercised	3.87
Weighted-Average Exercise Price, Forfeitures	11.12
Weighted-Average Exercise Price, Outstanding, Ending Balance	9.12	$ 6.36
Weighted-Average Exercise Price, Exercisable	$ 6.47
Weighted-Average Remaining Contractual Term, Outstanding	8 years 2 months 12 days	8 years 1 month 6 days
Weighted-Average Remaining Contractual Term, Exercisable	7 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding	$ 20.5	$ 36.6
Aggregate Intrinsic Value, Exercisable	$ 11.9

In-Process Research and Devel_2

In-Process Research and Development - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020
Research And Development [Abstract]
Impairment of in-process research and development	$ 22,100
In-process research and development - held for sale	$ 4,500	$ 4,500

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	Aug. 07, 2020	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Class Of Warrant Or Right [Line Items]
Net proceeds from common stock			$ 48,372	$ 0
Sale of securities	$ 300,000
At-the-market Sales (“ATM”)
Class Of Warrant Or Right [Line Items]
Gross proceeds from common stock		$ 50,000
Net proceeds from common stock	$ 100,000	$ 48,500
At-the-market Sales (“ATM”) | Common Stock at Purchase Price of $12.00 Per Share
Class Of Warrant Or Right [Line Items]
Number of shares sold		3.6
Purchase price per share		$ 12
At-the-market Sales (“ATM”) | Common Stock at Purchase Price of $12.70 Per Share
Class Of Warrant Or Right [Line Items]
Number of shares sold		0.5
Purchase price per share		$ 12.70