Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Total		Purchase Agreement Gilead	Common Stock		Common Stock Purchase Agreement Gilead	Additional Paid-In Capital	Additional Paid-In Capital Purchase Agreement Gilead	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2019	[1]	$ 163,842			$ 4			$ 369,100		$ (205,326)	$ 64
Balance, shares at Dec. 31, 2019	[1]				44,212,195
Issuance of common stock upon exercise of stock options		643						643
Issuance of common stock upon exercise of stock options, shares					59,939
Vesting of early exercised stock options		220						220
Vesting of early exercised stock options, shares					77,388
Stock-based compensation		3,462						3,462
Other comprehensive income (loss)		224									224
Net loss		(27,753)								(27,753)
Balance at Mar. 31, 2020		140,638			$ 4			373,425		(233,079)	288
Balance, shares at Mar. 31, 2020					44,349,522
Balance at Dec. 31, 2020	[1]	$ 502,304	[2]		$ 6			830,438		(328,184)	44
Balance, shares at Dec. 31, 2020		65,114,685			63,691,901	[1]
Issuance of common stock and rights to purchase additional shares in accordance with Amended and Restated Gilead Purchase Agreement, net of $55 offering costs				$ 220,296			$ 1		$ 220,295
Issuance of common stock and rights to purchase additional shares in accordance with Amended and Restated Gilead Purchase Agreement, net of $55 offering costs, Shares							5,650,000
Issuance of common stock upon exercise of stock options and vesting of restricted stock		$ 1,885						1,885
Issuance of common stock upon exercise of stock options and vesting of restricted stock, shares					200,828
Vesting of early exercised stock options		183						183
Vesting of early exercised stock options, shares					54,039
Stock-based compensation		12,761						12,761
Other comprehensive income (loss)		(46)									(46)
Net loss		(72,593)								(72,593)
Balance at Mar. 31, 2021		$ 664,790			$ 7			$ 1,065,562		$ (400,777)	$ (2)
Balance, shares at Mar. 31, 2021		70,965,513			69,596,768

[1] The balances as of December 31, 2020 and 2019 have been derived from the audited financial statements as of that date.

[2] The Condensed Consolidated Balance Sheet as of December 31, 2020 has been derived from the audited financial statements as of that date.