Consolidated Statements of Shareholders' Deficit - 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	6,207			6,207
Issuance of common stock under 2013 Equity Plan	605			605
Issuance of common stock under 2013 Equity Plan (in shares)			94
Issuance of common stock under ESPP	512			512
Issuance of common stock under ESPP (in shares)			114
Net income (loss)	(39,421)				(39,421)
Ending Balance at Dec. 31, 2020	(88,087)	$ 3,906	$ 3	984,756	(1,076,752)
Ending Balance (in shares) at Dec. 31, 2020		4	27,403
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	4,477			4,477
Issuance of common stock under 2013 Equity Plan	$ 156			156
Issuance of common stock under 2013 Equity Plan (in shares)	29,677		30
Issuance of common stock under ESPP	$ 436			436
Issuance of common stock under ESPP (in shares)			120
Purchases of common stock under Stock Repurchase Plan	(3,380)			(3,380)
Purchases of common stock under Stock Repurchase Plan (in shares)			(769)
Net income (loss)	19,660				19,660
Ending Balance at Dec. 31, 2021	$ (66,738)	$ 3,906	$ 3	$ 986,445	$ (1,057,092)
Ending Balance (in shares) at Dec. 31, 2021		4	26,784