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	$ 163,842		$ 4		$ 369,100		$ (205,326)	$ 64
Balance, shares at Dec. 31, 2019			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, 2019	163,842		$ 4		369,100		(205,326)	64
Balance, shares at Dec. 31, 2019			44,212,195
Net loss	(72,827)
Balance at Jun. 30, 2020	428,710		$ 6		706,713		(278,153)	144
Balance, shares at Jun. 30, 2020			57,372,168
Balance at Mar. 31, 2020	140,638		$ 4		373,425		(233,079)	288
Balance, shares at Mar. 31, 2020			44,349,522
Issuance of common stock	326,246		$ 2		326,244
Issuance of common stock, shares			12,650,000
Issuance of common stock upon exercise of stock options	1,751				1,751
Issuance of common stock upon exercise of stock options, shares			216,286
Vesting of early exercised stock options	216				216
Vesting of early exercised stock options, shares			64,501
Issuance of common stock under Employee Stock Purchase Plan	607				607
Issuance of common stock under Employee Stock Purchase Plan, shares			91,859
Stock-based compensation	4,470				4,470
Other comprehensive income (loss)	(144)							(144)
Net loss	(45,074)						(45,074)
Balance at Jun. 30, 2020	428,710		$ 6		706,713		(278,153)	144
Balance, shares at Jun. 30, 2020			57,372,168
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 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			69,596,768
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
Net loss	$ (148,563)
Balance at Jun. 30, 2021	$ 604,555		$ 7		1,081,341		(476,747)	(46)
Balance, shares at Jun. 30, 2021	71,374,059		70,042,790
Balance at Mar. 31, 2021	$ 664,790		$ 7		1,065,562		(400,777)	(2)
Balance, shares at Mar. 31, 2021			69,596,768
Issuance of common stock upon exercise of stock options and vesting of restricted stock	843				843
Issuance of common stock upon exercise of stock options and vesting of restricted stock, shares			269,369
Vesting of early exercised stock options	175				175
Vesting of early exercised stock options, shares			36,245
Issuance of common stock under Employee Stock Purchase Plan	1,394				1,394
Issuance of common stock under Employee Stock Purchase Plan, shares			140,408
Stock-based compensation	13,367				13,367
Other comprehensive income (loss)	(44)							(44)
Net loss	(75,970)						(75,970)
Balance at Jun. 30, 2021	$ 604,555		$ 7		$ 1,081,341		$ (476,747)	$ (46)
Balance, shares at Jun. 30, 2021	71,374,059		70,042,790