Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Offering	Offering Series B Convertible Preferred Stock	Common Stock	Common Stock Offering	Preferred Stock	Preferred Stock Offering Series B Convertible Preferred Stock	Additional Paid-in Capital	Additional Paid-in Capital Offering	Additional Paid-in Capital Offering Series B Convertible Preferred Stock	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Beginning Balances at Dec. 31, 2017	$ 199,549			$ 62				$ 1,107,693			$ (881)	$ (907,325)
Beginning Balances (in shares) at Dec. 31, 2017				61,533
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net	(523)			$ 1				(524)
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net (in shares)				1,204
Issuance of common stock under Employee Stock Purchase Plan	594							594
Issuance of common stock under Employee Stock Purchase Plan (in shares)				125
Stock compensation expense	23,478							23,478
Total other comprehensive loss	(1,134)										(1,134)
Net loss	(158,899)											(158,899)
Ending Balances at Dec. 31, 2018	63,065			$ 63				1,131,241			(2,015)	(1,066,224)
Ending Balances (in shares) at Dec. 31, 2018				62,862
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net	2			$ 1				1
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net (in shares)				975
Issuance of common stock under Employee Stock Purchase Plan	565							565
Issuance of common stock under Employee Stock Purchase Plan (in shares)				122
Issuance of common stock and preferred stock, net of issuance costs	60,113		$ 12,061	$ 20				60,093		$ 12,061
Issuance of common stock and preferred stock, net of issuance costs (in shares)				19,912			5
Stock compensation expense	25,456							25,456
Total other comprehensive loss	(372)										(372)
Net loss	(152,600)											(152,600)
Ending Balances at Dec. 31, 2019	8,290			$ 84				1,229,417			(2,387)	(1,218,824)
Ending Balances (in shares) at Dec. 31, 2019				83,871		5
Conversion of Preferred Stock	1			$ 1
Stock Issued During Period, Shares, Conversion of Convertible Securities				700
Stock Redeemed During Period, Shares, Conversion of Convertible Securities (in shares)						(1)
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net	289			$ 1				288
Issuance (withholding) of common stock upon exercise of stock options and restricted stock awards, net (in shares)				1,209
Issuance of common stock under Employee Stock Purchase Plan	672							672
Issuance of common stock under Employee Stock Purchase Plan (in shares)				195
Issuance of common stock and preferred stock, net of issuance costs		$ 108,537			$ 24				$ 108,513
Issuance of common stock and preferred stock, net of issuance costs (in shares)					24,215
Stock compensation expense	13,484							13,484
Total other comprehensive loss	2,660										2,660
Net loss	(75,240)											(75,240)
Ending Balances at Dec. 31, 2020	$ 58,693			$ 110				$ 1,352,374			$ 273	$ (1,294,064)
Ending Balances (in shares) at Dec. 31, 2020				110,190		4