Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2017	$ 1,126	$ 1,126
Balance at Dec. 31, 2017			$ 984	$ 714,869	$ (243)	$ (631,843)	$ 83,767
Net loss						(101,252)	(101,252)
Other comprehensive income (loss)					(54)		(54)
Exercise of stock options, net			11	2,490			2,501
Employee stock purchase plan sales, net			1	350			351
Issuance of common stock, net			105	53,295			53,400
Stock-based compensation expense				9,396			9,396
Balance (Accounting Standards Update 2016-02 [Member]) at Dec. 31, 2018	$ 238	$ 238
Balance at Dec. 31, 2018			1,101	780,400	(297)	(731,969)	49,235
Net loss						(108,897)	(108,897)
Other comprehensive income (loss)					336		336
Exercise of stock options, net			3	832			835
Employee stock purchase plan sales, net			1	403			404
Issuance of common stock, net			436	58,064			58,500
Stock-based compensation expense				17,719			17,719
Issuance of pre-funded warrants				19,882			19,882
Balance at Dec. 31, 2019			1,541	877,300	39	(840,628)	38,252
Net loss						(182,814)	(182,814)
Other comprehensive income (loss)					(36)		(36)
Exercise of stock options, net			5	1,809			1,814
Employee stock purchase plan sales, net			3	629			632
Issuance of common stock, net			220	93,059			93,279
Stock-based compensation expense				14,794			14,794
Issuance of pre-funded warrants				14,817			14,817
Balance at Dec. 31, 2020			$ 1,769	$ 1,002,408	$ 3	$ (1,023,442)	$ (19,262)