Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED DEFICIT
Beginning balance (in shares) at Dec. 31, 2018		45,478,883
Beginning balance, value at Dec. 31, 2018	$ 227,806	$ 45	$ 924,180	$ 0	$ (696,419)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)		612,759
Issuance of common stock upon exercise of stock options and warrants	3,140		3,140
Issuance of common stock upon exercise of stock purchase rights (in shares)		42,611
Issuance of common stock upon exercise of stock purchase rights	979		979
Issuance of common stock for restricted stock awards, net (in shares)		330,416
Issuance of common stock for restricted stock awards, net	(2,629)	$ 1	(2,630)
Stock-based compensation	45,551		45,551
Other comprehensive income (loss)	(92)			(92)
Equity component of Convertible Notes, net of issuance costs of $3,725	124,666		124,666
Payment for capped call share options	(32,890)		(32,890)
Net loss	(199,581)			0	(199,581)
Ending balance (in shares) at Dec. 31, 2019		46,464,669
Ending balance, value at Dec. 31, 2019	166,950	$ 46	1,062,996	(92)	(896,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)		51,333
Issuance of common stock upon exercise of stock options and warrants	172	$ 1	171
Issuance of common stock upon exercise of stock purchase rights (in shares)		60,857
Issuance of common stock upon exercise of stock purchase rights	724		724
Issuance of common stock for restricted stock awards, net (in shares)		244,785
Issuance of common stock for restricted stock awards, net	(1,754)		(1,754)
Stock-based compensation	40,937		40,937
Other comprehensive income (loss)	40			40
Net loss	(183,101)				(183,101)
Ending balance (in shares) at Dec. 31, 2020		46,821,644
Ending balance, value at Dec. 31, 2020	$ 23,968	$ 47	1,103,074	(52)	(1,079,101)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options and warrants (in shares)	1,146,095	1,135,607
Issuance of common stock upon exercise of stock options and warrants	$ 3,491	$ 1	3,490
Issuance of common stock upon exercise of stock purchase rights (in shares)		119,414
Issuance of common stock upon exercise of stock purchase rights	1,176		1,176
Issuance of common stock for restricted stock awards, net (in shares)		367,808
Issuance of common stock for restricted stock awards, net	(1,695)		(1,695)
Stock-based compensation	30,611		30,611
Other comprehensive income (loss)	(74)			(74)
Net loss	(74,810)				(74,810)
Ending balance (in shares) at Dec. 31, 2021		48,444,473
Ending balance, value at Dec. 31, 2021	$ (17,333)	$ 48	$ 1,136,656	$ (126)	$ (1,153,911)