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
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 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under 2013 Equity Plan (in shares)			44
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]
Net income (loss)	(24,183)
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]
Net income (loss)	(24,183)
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
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
Issuance of common stock under 2013 Equity Plan (in shares)			50
Issuance of common stock under ESPP	159			159
Issuance of common stock under ESPP (in shares)			32
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	27,359
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 ESPP	159			159
Issuance of common stock under ESPP (in shares)			32
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	27,359
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under 2013 Equity Plan (in shares)			50
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 (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
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 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under 2013 Equity Plan (in shares)			29
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]
Issuance of common stock under 2013 Equity Plan (in shares)	29,379
Net income (loss)	$ 18,151
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	27,482
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	18,151
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	27,482
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under 2013 Equity Plan (in shares)	29,379
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	27,449
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
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	27,482
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
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	27,482