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		4,000	27,195,000
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)			44,000
Issuance of common stock under ESPP	200			200
Issuance of common stock under ESPP (in shares)			38,000
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		4,000	27,277,000
Beginning Balance at Dec. 31, 2019	(55,990)	$ 3,906	$ 3	977,432	(1,037,331)
Beginning Balance (in shares) at Dec. 31, 2019		4,000	27,195,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (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		4,000	27,378,000
Beginning Balance at Mar. 31, 2020	(61,669)	$ 3,906	$ 3	980,344	(1,045,922)
Beginning Balance (in shares) at Mar. 31, 2020		4,000	27,277,000
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
Issuance of common stock under 2013 Equity Plan (in shares)			50,000
Issuance of common stock under ESPP	159			159
Issuance of common stock under ESPP (in shares)			32,000
Net income (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		4,000	27,359,000
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)			19,000
Net income (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		4,000	27,378,000
Beginning Balance at Dec. 31, 2020	(88,087)	$ 3,906	$ 3	984,756	(1,076,752)
Beginning Balance (in shares) at Dec. 31, 2020		4,000	27,403,000
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
Issuance of common stock under ESPP	81			81
Issuance of common stock under ESPP (in shares)			17,000
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		4,000	27,449,000
Beginning Balance at Dec. 31, 2020	$ (88,087)	$ 3,906	$ 3	984,756	(1,076,752)
Beginning Balance (in shares) at Dec. 31, 2020		4,000	27,403,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under 2013 Equity Plan (in shares)	29,677
Net income (loss)	$ 15,891
Ending Balance at Sep. 30, 2021	(68,408)	$ 3,906	$ 3	988,544	(1,060,861)
Ending Balance (in shares) at Sep. 30, 2021		4,000	27,518,000
Beginning Balance at Mar. 31, 2021	(72,318)	$ 3,906	$ 3	986,107	(1,062,334)
Beginning Balance (in shares) at Mar. 31, 2021		4,000	27,449,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,024			1,024
Issuance of common stock under 2013 Equity Plan	1			1
Issuance of common stock under ESPP	117			117
Issuance of common stock under ESPP (in shares)			33,000
Net income (loss)	3,733				3,733
Ending Balance at Jun. 30, 2021	(67,443)	$ 3,906	$ 3	987,249	(1,058,601)
Ending Balance (in shares) at Jun. 30, 2021		4,000	27,482,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	1,175			1,175
Issuance of common stock under 2013 Equity Plan	1			1
Issuance of common stock under ESPP	119			119
Issuance of common stock under ESPP (in shares)			36,000
Net income (loss)	(2,260)				(2,260)
Ending Balance at Sep. 30, 2021	$ (68,408)	$ 3,906	$ 3	$ 988,544	$ (1,060,861)
Ending Balance (in shares) at Sep. 30, 2021		4,000	27,518,000