Condensed Consolidated Statements of Stockholders' Deficit (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock Series C-1 Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
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
Issuance of common stock under ESPP	81			81
Issuance of common stock under ESPP (in shares)			17
Net income	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
Beginning Balance at Dec. 31, 2021	(66,738)	$ 3,906	$ 3	986,445	(1,057,092)
Beginning Balance (in shares) at Dec. 31, 2021		4	26,784
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,262			1,262
Issuance of common stock under ESPP	159			159
Issuance of common stock under ESPP (in shares)			42
Purchases of common stock under Stock Repurchase Plan	(5,179)			(5,179)
Purchases of common stock under Stock Repurchase Plan (in shares)			(1,162)
Net income	2				2
Ending Balance at Mar. 31, 2022	$ (70,494)	$ 3,906	$ 3	$ 982,687	$ (1,057,090)
Ending Balance (in shares) at Mar. 31, 2022		4	25,664