Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)		61,590,013
Beginning balance at Dec. 31, 2019	$ 109,952	$ 62	$ 778,693	$ 35	$ (668,838)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,326		1,326
Employee stock purchase plan purchases	229		229
Employee stock purchase plan purchases (in shares)		177,193
RSU stock issuance (in shares)		163,133
Comprehensive loss:
Unrealized loss on investments, net	(46)			(46)
Net loss	(10,420)				(10,420)
Comprehensive loss	(10,466)
Ending balance at Mar. 31, 2020	101,041	$ 62	780,248	(11)	(679,258)
Ending balance (in shares) at Mar. 31, 2020		61,930,339
Beginning balance at Dec. 31, 2019	109,952	$ 62	778,693	35	(668,838)
Comprehensive loss:
Unrealized loss on investments, net	95
Net loss	(20,436)
Comprehensive loss	(20,341)
Ending balance at Jun. 30, 2020	93,135	$ 62	782,217	130	(689,274)
Ending balance (in shares) at Jun. 30, 2020		62,172,418
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)		61,930,339
Beginning balance at Mar. 31, 2020	101,041	$ 62	780,248	(11)	(679,258)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	1,391		1,391
Exercise of stock options	578		578
Exercise of stock options (in shares)		242,079
Comprehensive loss:
Unrealized loss on investments, net	141			141
Net loss	(10,016)				(10,016)
Comprehensive loss	(9,875)
Ending balance at Jun. 30, 2020	93,135	$ 62	782,217	130	(689,274)
Ending balance (in shares) at Jun. 30, 2020		62,172,418
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)		62,172,418
Beginning balance (in shares)		62,816,039
Beginning balance at Dec. 31, 2020	73,376	$ 63	785,673	0	(712,360)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	2,584		2,584
Exercise of stock options	3,530	$ 1	3,529
Exercise of stock options (in shares)		710,132
Employee stock purchase plan purchases	330		330
Employee stock purchase plan purchases (in shares)		259,837
RSU stock issuance (in shares)		168,752
Issuance of common stock related to asset acquisition	43,445	$ 9	43,436
Issuance of common stock related to asset acquisition (in shares)		8,723,769
Issuance of common stock, net of issuance costs of $7.2 million	107,842	$ 13	107,829
Issuance of common stock, net of issuance costs $7.2 million (in shares)		13,529,750
Comprehensive loss:
Unrealized loss on investments, net	(43)			(43)
Net loss	(97,415)				(97,415)
Comprehensive loss	(97,458)
Ending balance at Mar. 31, 2021	133,649	$ 86	943,381	(43)	(809,775)
Ending balance (in shares) at Mar. 31, 2021		86,208,279
Beginning balance at Dec. 31, 2020	73,376	$ 63	785,673	0	(712,360)
Comprehensive loss:
Unrealized loss on investments, net	(11)
Net loss	(115,178)
Comprehensive loss	(115,189)
Ending balance at Jun. 30, 2021	119,149	$ 86	946,612	(11)	(827,538)
Ending balance (in shares) at Jun. 30, 2021		86,249,744
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)		86,208,279
Beginning balance at Mar. 31, 2021	133,649	$ 86	943,381	(43)	(809,775)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,112		3,112
Exercise of stock options	119		119
Exercise of stock options (in shares)		41,465
Comprehensive loss:
Unrealized loss on investments, net	32			32
Net loss	(17,763)				(17,763)
Comprehensive loss	(17,731)
Ending balance at Jun. 30, 2021	$ 119,149	$ 86	$ 946,612	$ (11)	$ (827,538)
Ending balance (in shares) at Jun. 30, 2021		86,249,744
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)		86,249,744