Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Purchase Agreement Gilead	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Common Stock Purchase Agreement Gilead	Additional Paid-In Capital	Additional Paid-In Capital Purchase Agreement Gilead	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2018	$ 234,942			$ 4		$ 357,873		$ (122,828)		$ (107)
Balance (ASC 606) at Dec. 31, 2018			$ 2,212						$ 2,212
Balance, shares at Dec. 31, 2018				43,610,823
Issuance of common stock upon exercise of stock options	188					188
Issuance of common stock upon exercise of stock options, shares				34,780
Vesting of early exercised stock options and restricted stock	1,029					1,029
Vesting of early exercised stock options and restricted stock, shares				417,883
Issuance of common stock under Employee Stock Purchase Plan	1,029					1,029
Issuance of common stock under Employee Stock Purchase Plan, shares				148,709
Stock-based compensation	8,981					8,981
Other comprehensive income (loss)	171									171
Net income (loss)	(84,710)							(84,710)
Balance at Dec. 31, 2019	163,842			$ 4		369,100		(205,326)		64
Balance, shares at Dec. 31, 2019				44,212,195
Issuance of common stock	326,246	$ 107,468		$ 2		326,244	$ 107,468
Issuance of common stock, shares		5,963,029		12,650,000	5,963,029
Issuance of common stock upon exercise of stock options and vesting of restricted stock	3,366					3,366
Issuance of common stock upon exercise of stock options and vesting of restricted stock, shares				405,752
Vesting of early exercised stock options	848					848
Vesting of early exercised stock options, shares				258,824
Issuance of common stock under Employee Stock Purchase Plan	1,587					1,587
Issuance of common stock under Employee Stock Purchase Plan, shares				202,101
Stock-based compensation	21,825					21,825
Other comprehensive income (loss)	(20)									(20)
Net income (loss)	(122,858)							(122,858)
Balance at Dec. 31, 2020	$ 502,304			$ 6		830,438		(328,184)		44
Balance, shares at Dec. 31, 2020	65,114,685			63,691,901
Issuance of common stock		$ 220,296			$ 1		$ 220,295
Issuance of common stock, shares					5,650,000
Issuance of common stock upon exercise of stock options, shares	680,755
Issuance of common stock upon exercise of stock options and vesting of restricted stock	$ 9,089					9,089
Issuance of common stock upon exercise of stock options and vesting of restricted stock, shares				1,045,423
Vesting of early exercised stock options	686					686
Vesting of early exercised stock options, shares				153,877
Issuance of common stock under Employee Stock Purchase Plan	3,022					3,022
Issuance of common stock under Employee Stock Purchase Plan, shares				230,589
Stock-based compensation	54,528					54,528
Other comprehensive income (loss)	(1,305)									(1,305)
Net income (loss)	52,830							52,830
Balance at Dec. 31, 2021	$ 841,450			$ 7		$ 1,118,058		$ (275,354)		$ (1,261)
Balance, shares at Dec. 31, 2021	70,781,736			70,771,790