Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 423,942	$ 11	$ 793,051	$ (601)	$ (368,519)
Beginning balance (in shares) at Dec. 31, 2019		107,648,925
Reclassification of derivative liability to additional paid-in capital	29,245		29,245
Vesting of restricted common stock	427		427
Vesting of restricted common stock (in shares)		618,079
Exercise of stock options	143		143
Exercise of stock option (in shares)		83,364
Stock-based compensation	2,967		2,967
Other comprehensive income (loss)	849			849
Net loss	(77,240)				(77,240)
Ending balance at Mar. 31, 2020	380,333	$ 11	825,833	248	(445,759)
Ending balance (in shares) at Mar. 31, 2020		108,350,368
Beginning balance at Dec. 31, 2020	$ 716,852	$ 13	1,385,301	(1,278)	(667,184)
Beginning balance (in shares) at Dec. 31, 2020	127,416,740	127,416,740
Issuance of common stock in connection with a collaboration agreement	$ 85,213		85,213
Issuance of common stock in connection with a collaboration agreement (in shares)		1,924,927
Vesting of restricted common stock (in shares)		52,963
Exercise of stock options	2,352		2,352
Exercise of stock option (in shares)		497,226
Stock-based compensation	15,471		15,471
Other comprehensive income (loss)	(26)			(26)
Net loss	(168,911)				(168,911)
Ending balance at Mar. 31, 2021	$ 650,951	$ 13	$ 1,488,337	$ (1,304)	$ (836,095)
Ending balance (in shares) at Mar. 31, 2021	129,891,856	129,891,856