Consolidated Statements of Shareholders' (Deficit) Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock Series C-1 Convertible Preferred Stock	Preferred Stock Series F Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance at Dec. 31, 2018	$ 35,921	$ 3,906	$ 2,737	$ 3	$ 950,258	$ (160)	$ (920,983)	$ 160
Beginning Balance (in shares) at Dec. 31, 2018		4	3	26,259
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	6,782				6,782
Issuance of common stock under ESPP	283				283
Issuance of common stock under ESPP (in shares)				52
Issuance of common stock for conversion of Series F Preferred Stock			$ (2,737)		2,737
Issuance of common stock for conversion of Series F Preferred Stock (in shares)			(3)	782
Net loss	(31,685)						(31,685)
Ending Balance at Mar. 31, 2019	11,301	$ 3,906		$ 3	959,900		(952,508)
Ending Balance (in shares) at Mar. 31, 2019		4		27,093
Beginning Balance at Dec. 31, 2018	35,921	$ 3,906	$ 2,737	$ 3	950,258	$ (160)	(920,983)	$ 160
Beginning Balance (in shares) at Dec. 31, 2018		4	3	26,259
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(91,275)
Ending Balance at Sep. 30, 2019	(35,171)	$ 3,906		$ 3	973,018		(1,012,098)
Ending Balance (in shares) at Sep. 30, 2019		4		27,147
Beginning Balance at Mar. 31, 2019	11,301	$ 3,906		$ 3	959,900		(952,508)
Beginning Balance (in shares) at Mar. 31, 2019		4		27,093
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	6,321				6,321
Issuance of common stock under ESPP	201				201
Issuance of common stock under ESPP (in shares)				32
Net loss	(30,416)						(30,416)
Ending Balance at Jun. 30, 2019	(12,593)	$ 3,906		$ 3	966,422		(982,924)
Ending Balance (in shares) at Jun. 30, 2019		4		27,125
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	6,419				6,419
Issuance of common stock under ESPP	177				177
Issuance of common stock under ESPP (in shares)				22
Net loss	(29,174)						(29,174)
Ending Balance at Sep. 30, 2019	(35,171)	$ 3,906		$ 3	973,018		(1,012,098)
Ending Balance (in shares) at Sep. 30, 2019		4		27,147
Beginning Balance at Dec. 31, 2019	(55,990)	$ 3,906		$ 3	977,432		(1,037,331)
Beginning Balance (in shares) at Dec. 31, 2019		4		27,195
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	2,407				2,407
Issuance of common stock under 2013 Equity Plan	305				305
Exercise of stock options for common stock (in shares)				44
Issuance of common stock under ESPP	200				200
Issuance of common stock under ESPP (in shares)				38
Net loss	(8,591)						(8,591)
Ending Balance at Mar. 31, 2020	(61,669)	$ 3,906		$ 3	980,344		(1,045,922)
Ending Balance (in shares) at Mar. 31, 2020		4		27,277
Beginning Balance at Dec. 31, 2019	$ (55,990)	$ 3,906		$ 3	977,432		(1,037,331)
Beginning Balance (in shares) at Dec. 31, 2019		4		27,195
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options for common stock (in shares)	94,219
Net loss	$ (35,943)
Ending Balance at Sep. 30, 2020	(85,515)	$ 3,906		$ 3	983,850		(1,073,274)
Ending Balance (in shares) at Sep. 30, 2020		4		27,378
Beginning Balance at Mar. 31, 2020	(61,669)	$ 3,906		$ 3	980,344		(1,045,922)
Beginning Balance (in shares) at Mar. 31, 2020		4		27,277
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,590				1,590
Issuance of common stock under 2013 Equity Plan	300				300
Exercise of stock options for common stock (in shares)				50
Issuance of common stock under ESPP	159				159
Issuance of common stock under ESPP (in shares)				32
Net loss	(15,592)						(15,592)
Ending Balance at Jun. 30, 2020	(75,212)	$ 3,906		$ 3	982,393		(1,061,514)
Ending Balance (in shares) at Jun. 30, 2020		4		27,359
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,388				1,388
Issuance of common stock under ESPP	69				69
Issuance of common stock under ESPP (in shares)				19
Net loss	(11,760)						(11,760)
Ending Balance at Sep. 30, 2020	$ (85,515)	$ 3,906		$ 3	$ 983,850		$ (1,073,274)
Ending Balance (in shares) at Sep. 30, 2020		4		27,378