Condensed Consolidated Statements of Shareholders' Deficit (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock Series C-1 Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
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
Issuance of common stock under 2013 Equity Plan (in shares)			44
Issuance of common stock under ESPP	200			200
Issuance of common stock under ESPP (in shares)			38
Net income (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, 2020	(88,087)	$ 3,906	$ 3	984,756	(1,076,752)
Beginning Balance (in shares) at Dec. 31, 2020		4	27,403
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,116			1,116
Issuance of common stock under 2013 Equity Plan	$ 154			154
Issuance of common stock under 2013 Equity Plan (in shares)	29,000		29
Issuance of common stock under ESPP	$ 81			81
Issuance of common stock under ESPP (in shares)			17
Net income (loss)	14,418				14,418
Ending Balance at Mar. 31, 2021	$ (72,318)	$ 3,906	$ 3	$ 986,107	$ (1,062,334)
Ending Balance (in shares) at Mar. 31, 2021		4	27,449