Unaudited Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock [Member] Series C-1 Convertible Preferred Stock [Member]	Preferred Stock [Member] Series F Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2017		4	3	22,167
Beginning Balance at Dec. 31, 2017	$ 88,202	$ 3,906	$ 2,737	$ 2	$ 803,071	$ (721,514)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	9,402				9,402
Issuance of common stock for conversion of Series F Preferred Stock (in shares)				3,910
Issuance of common stock for conversion of Series F Preferred Stock	109,809			$ 1	109,808
Exercise of stock options for common stock (in shares)				77
Exercise of stock options for common stock	528				528
Net loss	(50,528)					(50,528)
Ending Balance (in shares) at Mar. 31, 2018		4	3	26,154
Ending Balance at Mar. 31, 2018	157,413	$ 3,906	$ 2,737	$ 3	922,809	(772,042)
Beginning Balance (in shares) at Dec. 31, 2017		4	3	22,167
Beginning Balance at Dec. 31, 2017	88,202	$ 3,906	$ 2,737	$ 2	803,071	(721,514)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(103,306)
Ending Balance (in shares) at Jun. 30, 2018		4	3	26,219
Ending Balance at Jun. 30, 2018	115,667	$ 3,906	$ 2,737	$ 3	933,841	(824,820)
Beginning Balance (in shares) at Mar. 31, 2018		4	3	26,154
Beginning Balance at Mar. 31, 2018	157,413	$ 3,906	$ 2,737	$ 3	922,809	(772,042)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	9,844				9,844
Exercise of stock options for common stock (in shares)				65
Exercise of stock options for common stock	1,188				1,188
Net loss	(52,778)					(52,778)
Ending Balance (in shares) at Jun. 30, 2018		4	3	26,219
Ending Balance at Jun. 30, 2018	115,667	$ 3,906	$ 2,737	$ 3	933,841	(824,820)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2018-07	0
Beginning Balance (in shares) at Dec. 31, 2018		4	3	26,259
Beginning Balance at Dec. 31, 2018	35,921	$ 3,906	$ 2,737	$ 3	950,258	(920,983)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	6,782				6,782
Issuance of common stock under ESPP (in shares)				52
Issuance of common stock under ESPP	283				283
Issuance of common stock for conversion of Series F Preferred Stock (in shares)			(3)	782
Issuance of common stock for conversion of Series F Preferred Stock			$ (2,737)		2,737
Net loss	(31,685)					(31,685)
Ending Balance (in shares) at Mar. 31, 2019		4	0	27,093
Ending Balance at Mar. 31, 2019	11,301	$ 3,906	$ 0	$ 3	959,900	(952,508)
Beginning Balance (in shares) at Dec. 31, 2018		4	3	26,259
Beginning Balance at Dec. 31, 2018	35,921	$ 3,906	$ 2,737	$ 3	950,258	(920,983)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(62,101)
Ending Balance (in shares) at Jun. 30, 2019		4	0	27,125
Ending Balance at Jun. 30, 2019	(12,593)	$ 3,906	$ 0	$ 3	966,422	(982,924)
Beginning Balance (in shares) at Mar. 31, 2019		4	0	27,093
Beginning Balance at Mar. 31, 2019	11,301	$ 3,906	$ 0	$ 3	959,900	(952,508)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense	6,321				6,321
Issuance of common stock under ESPP (in shares)				32
Issuance of common stock under ESPP	201				201
Net loss	(30,416)					(30,416)
Ending Balance (in shares) at Jun. 30, 2019		4	0	27,125
Ending Balance at Jun. 30, 2019	(12,593)	$ 3,906	$ 0	$ 3	$ 966,422	$ (982,924)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2018-07	$ (160)