CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Balance at beginning of period (shares) at Dec. 31, 2017		28,622,886
Balance at beginning of period at Dec. 31, 2017	$ 143,288	$ 29	$ 594,407	$ 9,479	$ (460,627)
Increase (Decrease) in Stockholders' Equity
Net loss	(98,418)				(98,418)
Issuance of common stock and warrants, net of issuance costs (shares)		3,162,500
Issuance of common stock and warrants, net of issuance costs	130,663	$ 3	130,660
Share-based compensation expense	15,854		15,854
Issuance of common stock from ESPP (shares)		21,536
Issuance of common stock from ESPP	442		442
Issuance of common stock under equity incentive plans (shares)		731,935
Issuance of common stock under equity incentive plans	9,747	$ 1	9,746
Unrealized gain (loss) on investments	0
Balance at end of period (shares) at Dec. 31, 2018		32,538,857
Balance at end of period at Dec. 31, 2018	201,576	$ 33	751,109	9,479	(559,045)
Increase (Decrease) in Stockholders' Equity
Net loss	(213,256)				(213,256)
Issuance of common stock and warrants, net of issuance costs (shares)		4,269,838
Issuance of common stock and warrants, net of issuance costs	327,830	$ 4	327,826
Share-based compensation expense	55,537		55,537
Issuance of common stock from ESPP (shares)		14,488
Issuance of common stock from ESPP	675		675
Issuance of common stock under equity incentive plans (shares)		569,146
Issuance of common stock under equity incentive plans	8,473	$ 1	8,472
Proceeds from disgorgement of shareholders' short-swing profits	$ 1,050		1,050
Net exercise of warrants (shares)	2,125,000	2,125,000
Net exercise of warrants	$ 0	$ 2	(2)
Unrealized gain (loss) on investments	$ 410			410
Balance at end of period (shares) at Dec. 31, 2019	39,517,329	39,517,329
Balance at end of period at Dec. 31, 2019	$ 382,295	$ 40	1,144,667	9,889	(772,301)
Increase (Decrease) in Stockholders' Equity
Net loss	(357,937)				(357,937)
Issuance of common stock and warrants, net of issuance costs (shares)		8,124,168
Issuance of common stock and warrants, net of issuance costs	1,203,576	$ 8	1,203,568
Share-based compensation expense	85,847		85,847
Issuance of common stock from ESPP (shares)		14,436
Issuance of common stock from ESPP	$ 1,206		1,206
Issuance of common stock under equity incentive plans (shares)	1,318,963	1,319,901
Issuance of common stock under equity incentive plans	$ 45,891	$ 1	45,890
Proceeds from disgorgement of shareholders' short-swing profits	$ 41		41
Net exercise of warrants (shares)	1,400,000	1,463,235
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	$ (130)			(130)
Balance at end of period (shares) at Dec. 31, 2020	50,439,069	50,439,069
Balance at end of period at Dec. 31, 2020	$ 1,360,789	$ 50	$ 2,481,218	$ 9,759	$ (1,130,238)