Constellation Pharmaceuticals (CNST) 10-Q 6 May 20 2020 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Trading Symbol	CNST
Entity Registrant Name	CONSTELLATION PHARMACEUTICALS INC
Entity Central Index Key	0001434418
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity File Number	001-38584
Entity Tax Identification Number	26-1741721
Entity Address, Address Line One	215 First Street
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	714-0555
Entity Common Stock, Shares Outstanding		41,838,071
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 190,464	$ 334,332
Marketable securities	168,385	49,602
Prepaid expenses and other current assets	2,817	3,055
Total current assets	361,666	386,989
Property and equipment, net	867	971
Restricted cash	425	425
Operating lease, right-of-use assets	10,103	10,745
Total assets	373,061	399,130
Current liabilities:
Accounts payable	3,558	7,278
Accrued expenses and other current liabilities	12,980	12,915
Current portion of lease liabilities - operating lease	2,747	2,562
Total current liabilities	19,285	22,755
Long-term debt, net of current portion and discount	29,681	29,642
Operating lease liabilities, net of current portion	8,016	8,759
Other long-term liabilities	553	390
Total liabilities	57,535	61,546
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued or outstanding at March 31, 2020 and December 31, 2019, respectively
Common stock, $0.0001 par value; 200,000,000 shares authorized at March 31, 2020 and December 31, 2019, respectively; 41,822,064 and 41,719,039 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively;	4	4
Additional paid-in capital	660,443	656,973
Accumulated other comprehensive loss	(90)	(6)
Accumulated deficit	(344,831)	(319,387)
Total stockholders' equity	315,526	337,584
Total liabilities and stockholders' equity	$ 373,061	$ 399,130

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	41,822,064	41,719,039
Common stock, shares outstanding	41,822,064	41,719,039

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses:
Research and development	$ 20,075	$ 15,677
General and administrative	5,908	4,429
Total operating expenses	25,983	20,106
Loss from operations	(25,983)	(20,106)
Other income (expense):
Interest income	1,404	755
Interest expense	(850)	(75)
Total other income (expense), net	554	680
Loss before income taxes	(25,429)	(19,426)
Income tax expense	15
Net loss	$ (25,444)	$ (19,426)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.61)	$ (0.75)
Weighted average number of common shares used in net loss per share attributable to common stockholders, basic and diluted	41,765,635	25,804,595
Comprehensive loss:
Net Loss	$ (25,444)	$ (19,426)
Other comprehensive gain (loss):
Unrealized gain (loss) on marketable securities	(84)	9
Total other comprehensive gain (loss):	(84)	9
Comprehensive loss	$ (25,528)	$ (19,417)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Gain [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ 104,158	$ 3	$ 337,992		$ (233,837)
Beginning balance, shares at Dec. 31, 2018		25,803,135
Stock-based compensation expense	1,313		1,313
Vesting of common stock issued upon early exercise of unvested options, shares		85
Stock option exercises	21		21
Stock option exercises, shares		3,754
Unrealized gain (loss) on marketable securities	9			$ 9
Net Loss	(19,426)				(19,426)
Ending balance at Mar. 31, 2019	86,075	$ 3	339,326	9	(253,263)
Ending balance, shares at Mar. 31, 2019		25,806,974
Beginning balance at Dec. 31, 2018	104,158	$ 3	337,992		(233,837)
Beginning balance, shares at Dec. 31, 2018		25,803,135
Net Loss	(85,600)
Ending balance at Dec. 31, 2019	337,584	$ 4	656,973	(6)	(319,387)
Ending balance, shares at Dec. 31, 2019		41,719,039
Stock-based compensation expense	2,559		2,559
Stock option exercises	911		911
Stock option exercises, shares		103,025
Unrealized gain (loss) on marketable securities	(84)			(84)
Net Loss	(25,444)				(25,444)
Ending balance at Mar. 31, 2020	$ 315,526	$ 4	$ 660,443	$ (90)	$ (344,831)
Ending balance, shares at Mar. 31, 2020		41,822,064

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (25,444)	$ (19,426)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	147	168
Stock-based compensation expense	2,559	1,313
Non-cash interest expense	202	18
Amortization and accretion on marketable securities	(156)	(212)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	238	128
Operating lease, right-of-use assets	642	690
Accounts payable	(3,720)	1,768
Accrued expenses and other current liabilities	60	(2,116)
Operating lease liabilities	(558)	(664)
Net cash used in operating activities	(26,030)	(18,333)
Cash flows from investing activities:
Purchase of marketable securities	(135,161)	(63,123)
Purchases of property and equipment	(38)	(234)
Proceeds from maturities and sales of marketable securities	16,450
Net cash used in investing activities	(118,749)	(63,357)
Cash flows from financing activities:
Proceeds from issuance of long-term debt		19,649
Payment of debt issuance costs		(125)
Proceeds from issuance of common stock upon stock option exercises	911	21
Net cash provided by financing activities	911	19,545
Net decrease in cash, cash equivalents and restricted cash	(143,868)	(62,145)
Cash, cash equivalents and restricted cash at beginning of period	334,757	115,017
Cash, cash equivalents and restricted cash at end of period	190,889	52,872
Supplemental disclosure of cash flow information:
Interest paid	648
Supplemental disclosure of noncash investing and financing information:
Purchases of property and equipment included in accounts payable and accrued expenses	$ 5	$ 216

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Constellation Pharmaceuticals, Inc. (“Constellation” or the “Company”) is a clinical-stage biopharmaceutical company using its expertise in epigenetics to discover and develop novel therapeutics that address serious unmet medical needs in patients with cancers associated with abnormal gene expression or drug resistance. The Company was incorporated in January 2008 as EpiGenetiX, Inc. under the laws of the State of Delaware. On March 31, 2008, the Company changed its name to Constellation Pharmaceuticals, Inc. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The accompanying financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations with the proceeds of sales of convertible preferred stock, payments received in connection with collaboration agreements, borrowings under loan agreements, and proceeds from sales of its common stock public and private offerings The Company has incurred losses since inception, including net losses of $25.4 million for the three months ended March 31, 2020, and $85.6 million for the year ended December 31, 2019. As of March 31, 2020, the Company had an accumulated deficit of $344.8 million. The Company expects to continue to generate operating losses in the foreseeable future. Based on the Company’s current operating plan, the Company expects that its cash, cash equivalents and marketable securities at March 31, 2020, will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of the interim financial statements. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding sooner than would otherwise be expected. There can be no assurance that the Company will be able to obtain additional funding on acceptable terms, if at all. The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Consolidated Financial Information The accompanying unaudited condensed consolidated financial statements as of March 31, 2020 and for the three months ended March 31, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim consolidated financial statements. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 (the “Annual Report”). The unaudited condensed consolidated financial statements include the accounts of Constellation Pharmaceuticals, Inc. and its wholly owned subsidiary, Constellation Securities Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of March 31, 2020, and results of operations for the three months ended March 31, 2020 and 2019, stockholders’ equity for the three months ended March 31, 2020 and 2019, and cash flows for the three months ended March 31, 2020 and 2019 have been made. The Company’s results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020. Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains most of its cash, cash equivalents and marketable securities at two accredited financial institutions in amounts that could exceed federally insured limits. Cash equivalents are invested in an institutional money market fund. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Summary of Significant Accounting Policies The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies,” to the Consolidated Financial Statements included in the Annual Report. There have been no material changes to the significant accounting policies previously disclosed in the Annual Report other than as noted below. Cash, Cash Equivalents and Restricted Cash Cash equivalents consists of highly liquid investments that are readily convertible into cash with original maturities of three months or less from the date of purchase. The Company has a policy of making investments only in government securities or with commercial institutions that have at least an investment grade credit rating. The Company invests its cash primarily in reverse repurchase agreements (RRAs), government securities and obligations, corporate debt securities and money market funds. RRAs are collateralized by deposits in the form of government securities and obligations for an amount not less than 102% of their value. The Company does not record an asset or liability as the Company is not permitted to sell or repledge the associated collateral. The Company has a policy that the collateral has at least the prevailing credit rating of US Government Treasuries and Agencies. The Company utilizes a third-party custodian to manage the exchange of funds and ensure that collateral received is maintained at 102% of the value of the RRAs on a daily basis. RRAs have stated maturities of less than 30 days. As of March 31, 2020, the Company classified $0.4 million as restricted cash related to a letter of credit issued as a security deposit in connection with Company's lease of its corporate office facilities (Note 10). Cash, cash equivalents and restricted cash consists of the following (in thousands): March 31, 2020 December 31, 2019 Cash and cash equivalents $ 190,464 $ 334,332 Restricted cash 425 425 Cash, cash equivalents and restricted cash $ 190,889 $ 334,757 Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 – Quoted prices in active markets for identical assets or liabilities. • Level 2 – Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The carrying value of the Company’s outstanding debt as of March 31, 2020 (see Note 7) approximated fair value (a Level 3 measurement) based on interest rates currently available to the Company. Recently adopted accounting pronouncements In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception . In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued , Intangibles - Goodwill and Other - Internal-Use Software . This ASU addresses the accounting for implementation, setup and other upfront costs paid by a customer in a cloud computing or hosting arrangement. The guidance aligns the accounting treatment of these costs incurred in a hosting arrangement treated as a service contract with the requirements for capitalization and amortization costs to develop or obtain internal-use software. The guidance is effective for fiscal years beginning after December 15, 2019 and early adoption is permitted. The guidance can be adopted either retrospectively or prospectively. The adoption of ASU 2018-15 on January 1, 2020 did not have a material impact on the Company’s financial position, results of operations or cash flows. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808), Clarifying the Interaction between Topic 808 and Topic 606. ASC 606 ASC 606 ASU 2018-18 The adoption of ASU 2018-18 on January 1, 2020 did not have a material impact on the Company’s financial position, results of operations or cash flows. In March 2019, the FASB issued ASU No. 2019-01, Leases (Topic 842) Codification Improvements Recently issued accounting pronouncements In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments for annual and interim periods beginning after December 15, 2022 In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes Income Taxes

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): March 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 185,473 $ — $ — $ 185,473 Commercial paper — 4,991 — 4,991 $ 185,473 $ 4,991 $ — $ 190,464 Marketable securities: Corporate debt securities $ — $ 42,927 $ — $ 42,927 Commercial paper — 95,244 — 95,244 Government securities — 30,214 — 30,214 Total $ — $ 168,385 $ — $ 168,385 December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 303,345 $ — $ — $ 303,345 Commercial paper — 8,986 — 8,986 Corporate debt securities — 2,001 — 2,001 Reverse Repurchase Agreements (RRAs) — 20,000 — 20,000 $ 303,345 $ 30,987 $ — $ 334,332 Marketable securities: Corporate debt securities $ — $ 12,748 $ — $ 12,748 Commercial paper — 26,808 — 26,808 Government securities — 10,046 — 10,046 Total $ — $ 49,602 $ — $ 49,602 Money market funds were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 1 measurement within the fair value hierarchy. During the three months ended March 31, 2020 and the year ended December 31, 2019, there were no

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2020
Cash And Cash Equivalents [Abstract]
Marketable Securities	4. Marketable Securities The following table summarizes the Company’s marketable securities and cash equivalents as of March 31, 2020, and December 31, 2019, respectively, March 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash equivalents: Money market funds $ 185,473 $ — $ — $ 185,473 Commercial paper 4,991 — — 4,991 Total cash equivalents $ 190,464 $ — $ — $ 190,464 Marketable securities: Corporate debt securities $ 43,208 $ — $ (281 ) $ 42,927 Commercial paper 95,244 — — 95,244 Government securities 30,023 191 — 30,214 Total marketable securities $ 168,475 $ 191 $ (281 ) $ 168,385 Total cash equivalents and marketable securities $ 358,939 $ 191 $ (281 ) $ 358,849 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash equivalents: Money market funds $ 303,345 $ — $ — $ 303,345 Commercial paper 8,986 — — 8,986 Corporate debt securities 2,001 — — 2,001 Reverse Repurchase Agreements (RRAs) 20,000 — — 20,000 Total cash equivalents $ 334,332 $ — $ — $ 334,332 Marketable securities: Corporate debt securities $ 12,753 $ — $ (5 ) $ 12,748 Commercial paper 26,808 — — 26,808 Government securities 10,047 — (1 ) 10,046 Total marketable securities $ 49,608 $ — $ (6 ) $ 49,602 Total cash equivalents and marketable securities $ 383,940 $ — $ (6 ) $ 383,934

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2020 December 31, 2019 Accrued employee compensation and benefits $ 1,636 $ 4,527 Accrued external research and development expense 10,626 7,707 Accrued professional fees 295 184 Other 423 497 $ 12,980 $ 12,915

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreement	6. Collaboration Agreement The Company has a collaboration agreement (the “LLS Agreement”) with the Leukemia and Lymphoma Society, (“LLS”) pursuant to which LLS committed to provide funding to the Company for research and development services, conditional on (i) the achievement of milestones in accordance with the LLS Agreement and (ii) equal funding being provided by the Company. Through December 31, 2019, the Company received funding totaling $7.3 million from LLS upon the achievement of specified milestones, which were recorded as a reduction of research and development expense. There was no additional funding received in the three months ended March 31, 2020. The LLS Agreement requires the Company to make payments to LLS upon the Company’s achievement of specified milestones that could total up to $25.0 million in aggregate (see Note 11).

Debt

Debt	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt	7. Debt On March 20, 2019, the Company entered into a loan agreement with Hercules (“the Loan Agreement”) as administrative and collateral agent, and various other lenders, The term loan bears interest at an annual rate equal to the greater of 8.55% and the prime rate of interest plus 2.55%. As of March 31, 2020 and December 31, 2019, debt payable consisted of the following (in thousands): March 31, 2020 December 31, 2019 Principal amount of term loans $ 30,000 $ 30,000 Debt discount current portion — — Less: Current portion — — Long-term debt, net of current portion 30,000 30,000 Debt discount net of current portion (319 ) (358 ) Long-term debt, net of discount and current portion $ 29,681 $ 29,642

Equity

Equity	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Equity	8. Equity Common Stock As of March 31, 2020, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 200,000,000 shares of common stock, $0.0001 par value per share. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the Company’s board of directors. No dividends have been declared or paid by the Company since its inception. Warrants to Purchase Common Stock As of March 31, 2020, the Company had outstanding warrants to purchase common stock as follows: Issuance Date Term (in years) Exercise Price Number of Common Shares Issuable under Warrant May 23, 2011 10 $ 1.55 61,868 June 28, 2013 10 $ 13.22 7,569 September 30, 2014 10 $ 13.22 15,139 84,576

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	9. Stock-Based Compensation 2018 Equity Incentive Plan In June 2018, the Company’s stockholders approved the 2018 Plan, which became effective on July 18, 2018. The 2018 Plan provides for the grant of incentive stock options, non-qualified options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2018 Plan was 3,025,101. The number of shares reserved shall be annually increased on January 1, 2019 and each January 1 thereafter through January 1, 2028 by the least of (i) 2,216,368 shares, (ii) 4% of the number of shares of the Company’s common stock outstanding on the first day of the year or (iii) an amount determined by the Company’s board of directors. The shares of common stock underlying any awards that are expired, forfeited, canceled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, repurchased or are otherwise terminated by the Company under the 2018 Plan or any predecessor plan such as the 2008 Equity Incentive Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. In January 2020, the shares available for issuance under the 2018 Plan were increased by 1,668,762 shares pursuant to the annual increase described above. As of March 31, 2020, 2,539,355 shares remained available for future issuance under the 2018 Plan. 2018 Employee Stock Purchase Plan In June 2018, the Company’s stockholders approved the 2018 Employee Stock Purchase Plan which became effective on July 18, 2018. A total of 272,504 shares of common stock were reserved for issuance under this plan. The number of shares reserved shall be annually increased on January 1, 2020 and each January 1 thereafter through January 1, 2028 by the least of (i) 545,008 shares, (ii) 1% of the number of shares of the Company’s common stock outstanding on the first day of the year or (iii) an amount determined by the Company’s board of directors. In January 2020, the shares available for issuance under the 2018 Plan were increased by 417,190 shares pursuant to the annual increase described above. As of March 31, 2020, 689,694 shares remained available for future issuance under the 2018 Plan. Stock Option Issuances The following is a summary of stock option activity for the three months ended March 31, 2020: Stock Options Weighted Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2019 4,211,068 $ 8.95 8.39 $ 160,689 Granted 865,235 $ 36.13 Exercised (103,025 ) $ 8.84 Forfeited (57,885 ) $ 11.89 Outstanding as of March 31, 2020 4,915,393 $ 13.70 8.45 $ 92,022 Vested and expected to vest at March 31, 2020 4,915,393 $ 13.70 8.45 $ 92,022 Exercisable at March 31, 2020 1,463,880 $ 7.50 7.60 $ 35,031 During the three months ended March 31, 2020, the Company granted options to employees and directors for the purchase of 865,235 shares of common stock with a weighted average exercise price of $36.13 per share and a weighted average grant-date fair value of $25.36 per share. The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Three Months Ended March 31, 2020 2019 Risk-free interest rate 1.46 % 2.49 % Expected volatility 82.17 % 82.13 % Expected dividend yield — — Expected term (in years) 6.06 6.06 As of March 31, 2020, total unrecognized compensation cost related to the unvested stock-based awards was $37.4 million, which is expected to be recognized over a weighted average period of 3.22 years. Stock-Based Compensation The Company recorded stock-based compensation expense in the following expense categories of its statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2020 2019 Research and development expenses $ 1,006 $ 524 General and administrative expenses 1,553 789 Total $ 2,559 $ 1,313

Leases

Leases	3 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Leases	10. Leases The Company has leases for office and laboratory space. The Company occupies approximately 47,546 square feet of office and laboratory space in Cambridge, Massachusetts under a lease that expires on June 30, 2023. The Company determined that these leases are operating leases. In June 2019, the Company entered into a sublease agreement for a portion of its office space consisting of approximately 4,422 square feet. The sub-lease commenced on June 21, 2019, (the “2019 sublease”) and expires on June 20, 2020. We recognize our minimum rental expense on a straight-line basis over the term of the lease beginning with the date of initial control of the asset. We recognized all leases with terms greater than 12 months in duration on our Condensed Consolidated Balance Sheets as right-of-use assets and lease liabilities.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Research Agreements The LLS Agreement requires the Company to make certain milestone payments to LLS, that could total up to $25.0 million in the aggregate, upon the receipt of payments by the Company associated with the licensing or transfer of rights to the related compound (or a product) to a third party, upon first regulatory approval of a product in the U.S., or upon the first regulatory approval of a product in Europe or Japan. As of March 31, 2020, and December 31, 2019, no events have occurred that would require payment of the milestones. The Company has several in-license agreements with academic organizations. The Company is obligated to pay annual license maintenance fees of less than $0.1 million per year as well as reimburse certain institutions for costs incurred related to the filing, prosecution and maintenance of patent rights licensed under the agreements. In addition, the Company may be obligated to pay contingent milestone payments of up to a maximum of $15.7 million upon the achievement of certain defined events as well as royalties of low single-digit percentages of sales of licensed products. In certain cases, the maximum payments to the academic organizations are capped. If the Company grants any sublicense rights under the license agreements, the Company has agreed to pay a percentage of sublicense fees received by the Company to the licensors. As of March 31, 2020, and December 31, 2019, no events have occurred that would require payment of the milestones, royalties, or sublicense fees. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its financial statements as of March 31, 2020 or December 31, 2019. Legal Proceedings The Company is not a party to any material legal matters or claims and did not have contingency reserves established for any litigation liabilities as of March 31, 2020 or December 31, 2019.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2020 2019 Numerator: Net loss $ (25,444 ) $ (19,426 ) Net loss attributable to common stockholders $ (25,444 ) $ (19,426 ) Denominator: Weighted average common shares outstanding, basic and diluted 41,765,635 25,804,595 Net loss per share attributable to common stockholders, basic and diluted $ (0.61 ) $ (0.75 ) The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2020 2019 Warrants for the purchase of common stock 84,576 95,930 Options to purchase common stock 4,915,393 4,712,054 4,999,969 4,807,984

Retirement Plan

Retirement Plan	3 Months Ended
	Mar. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Retirement Plan	13. Retirement Plan The Company has a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. As currently established, the Company is not required to make contributions to the 401(k) Plan. The Company made matching contributions of $0.2 million and $0.1 million for each of the three months ended March 31, 2020 and 2019, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Unaudited interim consolidated financial information	Unaudited Interim Consolidated Financial Information The accompanying unaudited condensed consolidated financial statements as of March 31, 2020 and for the three months ended March 31, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim consolidated financial statements. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 (the “Annual Report”). The unaudited condensed consolidated financial statements include the accounts of Constellation Pharmaceuticals, Inc. and its wholly owned subsidiary, Constellation Securities Corporation. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of March 31, 2020, and results of operations for the three months ended March 31, 2020 and 2019, stockholders’ equity for the three months ended March 31, 2020 and 2019, and cash flows for the three months ended March 31, 2020 and 2019 have been made. The Company’s results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020.
Concentrations of credit risk and of significant suppliers	Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains most of its cash, cash equivalents and marketable securities at two accredited financial institutions in amounts that could exceed federally insured limits. Cash equivalents are invested in an institutional money market fund. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
Cash, cash equivalents and restricted cash	Cash, Cash Equivalents and Restricted Cash Cash equivalents consists of highly liquid investments that are readily convertible into cash with original maturities of three months or less from the date of purchase. The Company has a policy of making investments only in government securities or with commercial institutions that have at least an investment grade credit rating. The Company invests its cash primarily in reverse repurchase agreements (RRAs), government securities and obligations, corporate debt securities and money market funds. RRAs are collateralized by deposits in the form of government securities and obligations for an amount not less than 102% of their value. The Company does not record an asset or liability as the Company is not permitted to sell or repledge the associated collateral. The Company has a policy that the collateral has at least the prevailing credit rating of US Government Treasuries and Agencies. The Company utilizes a third-party custodian to manage the exchange of funds and ensure that collateral received is maintained at 102% of the value of the RRAs on a daily basis. RRAs have stated maturities of less than 30 days. As of March 31, 2020, the Company classified $0.4 million as restricted cash related to a letter of credit issued as a security deposit in connection with Company's lease of its corporate office facilities (Note 10). Cash, cash equivalents and restricted cash consists of the following (in thousands): March 31, 2020 December 31, 2019 Cash and cash equivalents $ 190,464 $ 334,332 Restricted cash 425 425 Cash, cash equivalents and restricted cash $ 190,889 $ 334,757
Fair value measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 – Quoted prices in active markets for identical assets or liabilities. • Level 2 – Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The carrying value of the Company’s outstanding debt as of March 31, 2020 (see Note 7) approximated fair value (a Level 3 measurement) based on interest rates currently available to the Company.
Recently adopted accounting pronouncements	Recently adopted accounting pronouncements In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815) I. Accounting for Certain Financial Instruments with Down Round Features II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception . In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued , Intangibles - Goodwill and Other - Internal-Use Software . This ASU addresses the accounting for implementation, setup and other upfront costs paid by a customer in a cloud computing or hosting arrangement. The guidance aligns the accounting treatment of these costs incurred in a hosting arrangement treated as a service contract with the requirements for capitalization and amortization costs to develop or obtain internal-use software. The guidance is effective for fiscal years beginning after December 15, 2019 and early adoption is permitted. The guidance can be adopted either retrospectively or prospectively. The adoption of ASU 2018-15 on January 1, 2020 did not have a material impact on the Company’s financial position, results of operations or cash flows. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808), Clarifying the Interaction between Topic 808 and Topic 606. ASC 606 ASC 606 ASU 2018-18 The adoption of ASU 2018-18 on January 1, 2020 did not have a material impact on the Company’s financial position, results of operations or cash flows. In March 2019, the FASB issued ASU No. 2019-01, Leases (Topic 842) Codification Improvements
Recently issued accounting pronouncements	Recently issued accounting pronouncements In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments for annual and interim periods beginning after December 15, 2022 In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes Income Taxes

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents and Restricted Cash	Cash, cash equivalents and restricted cash consists of the following (in thousands): March 31, 2020 December 31, 2019 Cash and cash equivalents $ 190,464 $ 334,332 Restricted cash 425 425 Cash, cash equivalents and restricted cash $ 190,889 $ 334,757

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): March 31, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 185,473 $ — $ — $ 185,473 Commercial paper — 4,991 — 4,991 $ 185,473 $ 4,991 $ — $ 190,464 Marketable securities: Corporate debt securities $ — $ 42,927 $ — $ 42,927 Commercial paper — 95,244 — 95,244 Government securities — 30,214 — 30,214 Total $ — $ 168,385 $ — $ 168,385 December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 303,345 $ — $ — $ 303,345 Commercial paper — 8,986 — 8,986 Corporate debt securities — 2,001 — 2,001 Reverse Repurchase Agreements (RRAs) — 20,000 — 20,000 $ 303,345 $ 30,987 $ — $ 334,332 Marketable securities: Corporate debt securities $ — $ 12,748 $ — $ 12,748 Commercial paper — 26,808 — 26,808 Government securities — 10,046 — 10,046 Total $ — $ 49,602 $ — $ 49,602

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2020
Cash And Cash Equivalents [Abstract]
Schedule of Marketable Securities and Cash Equivalents	The following table summarizes the Company’s marketable securities and cash equivalents as of March 31, 2020, and December 31, 2019, respectively, March 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash equivalents: Money market funds $ 185,473 $ — $ — $ 185,473 Commercial paper 4,991 — — 4,991 Total cash equivalents $ 190,464 $ — $ — $ 190,464 Marketable securities: Corporate debt securities $ 43,208 $ — $ (281 ) $ 42,927 Commercial paper 95,244 — — 95,244 Government securities 30,023 191 — 30,214 Total marketable securities $ 168,475 $ 191 $ (281 ) $ 168,385 Total cash equivalents and marketable securities $ 358,939 $ 191 $ (281 ) $ 358,849 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Cash equivalents: Money market funds $ 303,345 $ — $ — $ 303,345 Commercial paper 8,986 — — 8,986 Corporate debt securities 2,001 — — 2,001 Reverse Repurchase Agreements (RRAs) 20,000 — — 20,000 Total cash equivalents $ 334,332 $ — $ — $ 334,332 Marketable securities: Corporate debt securities $ 12,753 $ — $ (5 ) $ 12,748 Commercial paper 26,808 — — 26,808 Government securities 10,047 — (1 ) 10,046 Total marketable securities $ 49,608 $ — $ (6 ) $ 49,602 Total cash equivalents and marketable securities $ 383,940 $ — $ (6 ) $ 383,934

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2020
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2020 December 31, 2019 Accrued employee compensation and benefits $ 1,636 $ 4,527 Accrued external research and development expense 10,626 7,707 Accrued professional fees 295 184 Other 423 497 $ 12,980 $ 12,915

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Components of Debt Payable	As of March 31, 2020 and December 31, 2019, debt payable consisted of the following (in thousands): March 31, 2020 December 31, 2019 Principal amount of term loans $ 30,000 $ 30,000 Debt discount current portion — — Less: Current portion — — Long-term debt, net of current portion 30,000 30,000 Debt discount net of current portion (319 ) (358 ) Long-term debt, net of discount and current portion $ 29,681 $ 29,642

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Schedule of Warrant Activities	As of March 31, 2020, the Company had outstanding warrants to purchase common stock as follows: Issuance Date Term (in years) Exercise Price Number of Common Shares Issuable under Warrant May 23, 2011 10 $ 1.55 61,868 June 28, 2013 10 $ 13.22 7,569 September 30, 2014 10 $ 13.22 15,139 84,576

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Company's Option Activity	The following is a summary of stock option activity for the three months ended March 31, 2020: Stock Options Weighted Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2019 4,211,068 $ 8.95 8.39 $ 160,689 Granted 865,235 $ 36.13 Exercised (103,025 ) $ 8.84 Forfeited (57,885 ) $ 11.89 Outstanding as of March 31, 2020 4,915,393 $ 13.70 8.45 $ 92,022 Vested and expected to vest at March 31, 2020 4,915,393 $ 13.70 8.45 $ 92,022 Exercisable at March 31, 2020 1,463,880 $ 7.50 7.60 $ 35,031
Schedule of Weighted Average Basis Assumptions Used in Black-Scholes Option-Pricing Model	The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions: Three Months Ended March 31, 2020 2019 Risk-free interest rate 1.46 % 2.49 % Expected volatility 82.17 % 82.13 % Expected dividend yield — — Expected term (in years) 6.06 6.06
Schedule of Stock Based Compensation Expense Related to Statements of Operations and Comprehensive Loss	The Company recorded stock-based compensation expense in the following expense categories of its statements of operations and comprehensive loss (in thousands): Three Months Ended March 31, 2020 2019 Research and development expenses $ 1,006 $ 524 General and administrative expenses 1,553 789 Total $ 2,559 $ 1,313

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Calculations of Basic and Diluted Net Loss per Share	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2020 2019 Numerator: Net loss $ (25,444 ) $ (19,426 ) Net loss attributable to common stockholders $ (25,444 ) $ (19,426 ) Denominator: Weighted average common shares outstanding, basic and diluted 41,765,635 25,804,595 Net loss per share attributable to common stockholders, basic and diluted $ (0.61 ) $ (0.75 )
Schedule of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2020 2019 Warrants for the purchase of common stock 84,576 95,930 Options to purchase common stock 4,915,393 4,712,054 4,999,969 4,807,984

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net losses	$ 25,444	$ 19,426	$ 85,600
Accumulated deficit	$ 344,831		$ 319,387

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Significant Accounting Policies [Line Items]
Percentage Securities for Reverse Repurchase Agreements	102.00%
Restricted cash	$ 425	$ 425
Letter of Credit [Member]
Significant Accounting Policies [Line Items]
Restricted cash	$ 400
Maximum [Member]
Significant Accounting Policies [Line Items]
Percentage Securities for Reverse Repurchase Agreements	102.00%
Reverse repurchase agreements maturity period	30 days

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 190,464	$ 334,332
Restricted cash	425	425
Cash, cash equivalents and restricted cash	$ 190,889	$ 334,757	$ 52,872	$ 115,017

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Cash equivalents:
Cash and cash equivalents	$ 190,464	$ 334,332
Marketable securities:
Marketable securities	168,385	49,602
Commercial Paper [Member]
Cash equivalents:
Cash and cash equivalents	4,991	8,986
Marketable securities:
Marketable securities	95,244	26,808
Government Securities [Member]
Marketable securities:
Marketable securities	30,214	10,046
Reverse Repurchase Agreements (RRAs)
Cash equivalents:
Cash and cash equivalents		20,000
Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash and cash equivalents	185,473	303,345
Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash and cash equivalents	4,991	30,987
Marketable securities:
Marketable securities	168,385	49,602
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Cash equivalents:
Cash and cash equivalents	4,991	8,986
Marketable securities:
Marketable securities	95,244	26,808
Fair Value, Inputs, Level 2 [Member] | Government Securities [Member]
Marketable securities:
Marketable securities	30,214	10,046
Fair Value, Inputs, Level 2 [Member] | Reverse Repurchase Agreements (RRAs)
Cash equivalents:
Cash and cash equivalents		20,000
Money Market Funds [Member]
Cash equivalents:
Cash and cash equivalents	185,473	303,345
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents:
Cash and cash equivalents	185,473	303,345
Corporate Debt Securities [Member]
Cash equivalents:
Cash and cash equivalents		2,001
Marketable securities:
Marketable securities	42,927	12,748
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents:
Cash and cash equivalents		2,001
Marketable securities:
Marketable securities	$ 42,927	$ 12,748

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair value of assets transfers level 1 to level 2	$ 0	$ 0
Fair value of assets transfers level 2 to level 1	0	0
Fair value of liabilities transfers level 1 to level 2	0	0
Fair value of liabilities transfers level 2 to level 1	$ 0	$ 0

Marketable Securities - Schedul

Marketable Securities - Schedule of Marketable Securities and Cash Equivalents (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Cash And Cash Equivalents [Line Items]
Amortized Cost	$ 358,939	$ 383,940
Unrealized Gains	191
Unrealized Losses	(281)	(6)
Fair Value	358,849	383,934
Total Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	190,464	334,332
Fair Value	190,464	334,332
Total marketable securities [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	168,475	49,608
Unrealized Gains	191
Unrealized Losses	(281)	(6)
Fair Value	168,385	49,602
Corporate Debt Securities [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	43,208	12,753
Unrealized Losses	(281)	(5)
Fair Value	42,927	12,748
Commercial Paper [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	95,244	26,808
Fair Value	95,244	26,808
Government Securities [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	30,023	10,047
Unrealized Gains	191
Unrealized Losses		(1)
Fair Value	30,214	10,046
Money Market Funds [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	185,473	303,345
Fair Value	185,473	303,345
Commercial Paper [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost	4,991	8,986
Fair Value	$ 4,991	8,986
Corporate Debt Securities [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost		2,001
Fair Value		2,001
Reverse Repurchase Agreements (RRAs) [Member]
Cash And Cash Equivalents [Line Items]
Amortized Cost		20,000
Fair Value		$ 20,000

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued employee compensation and benefits	$ 1,636	$ 4,527
Accrued external research and development expense	10,626	7,707
Accrued professional fees	295	184
Other	423	497
Accrued expenses and other current liabilities	$ 12,980	$ 12,915

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - LLS Agreement [Member] - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone method revenue recognized	$ 0	$ 7,300,000
Milestone payments maximum amount	$ 25,000,000

Debt - Additional Information (

Debt - Additional Information (Detail) - Loan Agreement [Member] - USD ($)	Mar. 20, 2019	Mar. 31, 2020
Debt Instrument [Line Items]
Loan amount		$ 30,000,000
Unused amount expired		$ 10,000,000
Debt instrument, interest rate terms	The term loan bears interest at an annual rate equal to the greater of 8.55% and the prime rate of interest plus 2.55%.
Frequency of periodic payment	The Loan Agreement provides for interest-only payments until April 30, 2021, and repayment of the aggregate outstanding principal balance of the term loan in monthly installments starting on May 1, 2021 and continuing through April 1, 2023 (the “Maturity Date”).
Loan Agreement maturity date	Apr. 1, 2023
Debt instrument, fee description	The Company paid a fee of $0.3 million upon closing and is required to pay a fee of 6.35% of the aggregate amount of advances under the Loan Agreement at maturity.
Debt instrument closing fee	$ 300,000
Debt instrument, redemption, description	At its option, the Company may elect to prepay all or a portion of the outstanding advances by paying the entire principal balance (or a portion thereof) and all accrued and unpaid interest thereon plus a prepayment charge equal to the following percentage of the principal amount being prepaid: 2% if an advance is prepaid during the first 12 months following the applicable advance date, 1% if an advance is prepaid after 12 months but prior to 24 months following the applicable advance date, and 0.5% if an advance is prepaid any time after 24 months following the applicable advance date but prior to the Maturity Date.
Maximum [Member]
Debt Instrument [Line Items]
Loan amount	$ 40,000,000

Debt - Components of Debt Payab

Debt - Components of Debt Payable (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
Principal amount of term loans	$ 30,000	$ 30,000
Long-term debt, net of current portion	30,000	30,000
Debt discount net of current portion	(319)	(358)
Long-term debt, net of discount and current portion	$ 29,681	$ 29,642

Equity - Additional Information

Equity - Additional Information (Detail) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock, shares authorized	200,000,000	200,000,000
Common stock, par value	$ 0.0001	$ 0.0001

Equity - Schedule of Warrant Ac

Equity - Schedule of Warrant Activities (Detail) - Common Stock [Member]	3 Months Ended
	Mar. 31, 2020$ / sharesshares
Class of Warrant or Right [Line Items]
Number of Common Shares Issuable under Warrant	84,576
Warrant One [Member]
Class of Warrant or Right [Line Items]
Warrant Issue date	May 23, 2011
Warrant Term	10 years
Warrants exercise price | $ / shares	$ 1.55
Number of Common Shares Issuable under Warrant	61,868
Warrant Two [Member]
Class of Warrant or Right [Line Items]
Warrant Issue date	Jun. 28, 2013
Warrant Term	10 years
Warrants exercise price | $ / shares	$ 13.22
Number of Common Shares Issuable under Warrant	7,569
Warrant Three [Member]
Class of Warrant or Right [Line Items]
Warrant Issue date	Sep. 30, 2014
Warrant Term	10 years
Warrants exercise price | $ / shares	$ 13.22
Number of Common Shares Issuable under Warrant	15,139

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Jan. 31, 2020	Jun. 30, 2018	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost related to unvested stock-based awards			$ 37.4
Unvested stock based weighted average period			3 years 2 months 19 days
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted			865,235
Weighted average exercise price			$ 36.13
Weighted average grant-date fair value per share			$ 25.36
2018 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		3,025,101
Shares remained available for future issuance			2,539,355
Number of shares increased reserved for issuance under plan	1,668,762
2018 Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock available for issuance		2,216,368
Percentage of shares of common stock available for issuance		4.00%
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		272,504
Shares remained available for future issuance			689,694
Number of shares increased reserved for issuance under plan	417,190
ESPP [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock available for issuance		545,008
Percentage of shares of common stock available for issuance		1.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Company's Option Activity (Detail) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning Balance	4,211,068
Number of Shares, Granted	865,235
Number of Shares, Exercised	(103,025)
Number of Shares, Forfeited	(57,885)
Number of Shares Outstanding, Ending Balance	4,915,393	4,211,068
Number of Shares, Vested and expected to vest	4,915,393
Number of Shares, Options exercisable	1,463,880
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 8.95
Weighted Average Exercise Price, Granted	36.13
Weighted Average Exercise Price, Exercised	8.84
Weighted Average Exercise Price, Forfeited	11.89
Weighted Average Exercise Price Outstanding, Ending Balance	13.70	$ 8.95
Weighted Average Exercise Price, Vested and expected to vest	13.70
Weighted Average Exercise Price, Options exercisable	$ 7.50
Weighted Average Contractual Term (in years) Outstanding	8 years 5 months 12 days	8 years 4 months 20 days
Weighted Average Contractual Term (in years), Vested and expected to vest	8 years 5 months 12 days
Weighted Average Contractual Term (in years), Options exercisable	7 years 7 months 6 days
Aggregate Intrinsic Value Outstanding, Beginning Balance	$ 92,022	$ 160,689
Aggregate Intrinsic Value, Vested and expected to vest	92,022
Exercisable at March 31, 2020	$ 35,031

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Weighted Average Basis Assumptions Used in Black-Scholes Option-Pricing Model (Detail) - Valuation Technique, Option Pricing Model	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.46%	2.49%
Expected volatility	82.17%	82.13%
Expected term (in years)	6 years 21 days	6 years 21 days

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Related to Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 2,559	$ 1,313
Research and Development Expenses [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	1,006	524
General and Administrative Expenses [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation	$ 1,553	$ 789

Leases - Additional Information

Leases - Additional Information (Detail) - ft²	1 Months Ended	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2020
Leases [Line Items]
Office and laboratory space		47,546
Lease expiration date		Jun. 30, 2023
2019 Sublease
Leases [Line Items]
Rentable office space under sublease	4,422
Sublease commencement date	Jun. 21, 2019
Sublease expiration date	Jun. 20, 2020

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments And Contingencies [Line Items]
License maintenance fees	$ 100,000
Contingent milestone payments	15,700,000
Contingency reserve for litigation liabilities	0	$ 0
LLS Agreement [Member]
Commitments And Contingencies [Line Items]
Milestone payments maximum amount	$ 25,000,000

Net Loss Per Share - Calculatio

Net Loss Per Share - Calculations of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Numerator:
Net Loss	$ (25,444)	$ (19,426)	$ (85,600)
Net loss attributable to common stockholders	$ (25,444)	$ (19,426)
Denominator:
Weighted average common shares outstanding, basic and diluted	41,765,635	25,804,595
Net loss per share attributable to common stockholders, basic and diluted	$ (0.61)	$ (0.75)

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	4,999,969	4,807,984
Warrants for the purchase of common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	84,576	95,930
Options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	4,915,393	4,712,054

Retirement Plan - Additional In

Retirement Plan - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Matching contributions made	$ 0.2	$ 0.1
Defined contribution plan name	401(k) Plan