Consolidated Statements of Stockholders' Deficit - USD ($) $ in Thousands	Total	At-the-market Placement	Public Offering	Note Payable to Related Party	Facility Financing Obligation	Senior Convertible Notes	Common Stock	Common Stock At-the-market Placement	Common Stock Public Offering	Common Stock Note Payable to Related Party	Common Stock Facility Financing Obligation	Common Stock Senior Convertible Notes	Additional Paid-in Capital	Additional Paid-in Capital At-the-market Placement	Additional Paid-in Capital Public Offering	Additional Paid-in Capital Note Payable to Related Party	Additional Paid-in Capital Facility Financing Obligation	Additional Paid-in Capital Senior Convertible Notes	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2015	$ (350,329)						$ 857						$ 2,512,063						$ (20)	$ (2,863,229)
Beginning Balance (in shares) at Dec. 31, 2015							85,735,000
Exercise of stock options	467						$ 1						466
Exercise of stock options (in shares)							55,000
Issuance of common shares from the release of restricted stock units	0						$ 1						(1)
Issuance of common shares from the release of restricted stock units (in shares)							131,000
Issuance of common shares under Employee Stock Purchase Plan	426						$ 1						425
Issuance of common shares under Employee Stock Purchase Plan (in shares)							51,000
Stock-based compensation expense	5,135												5,135
Restricted stock units taxes paid in cash	(165)												(165)
Issuance of direct placement — common stock and warrants	50,000						$ 97						49,903
Issuance of direct placement - common stock and warrants (in shares)							9,709,000
Issuance costs associated with direct placement	(2,037)												(2,037)
Proceeds allocated to warrant liabilities	(12,750)												(12,750)
Cumulative translation (loss) gain	(4)																		(4)
Net (loss) income	125,664																			125,664
Ending Balance at Dec. 31, 2016	(183,593)						$ 957						2,553,039						(24)	(2,737,565)
Ending Balance (in shares) at Dec. 31, 2016							95,681,000
Exercise of stock options	24												24
Exercise of stock options (in shares)							5,000
Issuance of common shares from the release of restricted stock units	1						$ 2						(1)
Issuance of common shares from the release of restricted stock units (in shares)							135,000
Issuance of common shares under Employee Stock Purchase Plan	236						$ 1						235
Issuance of common shares under Employee Stock Purchase Plan (in shares)							103,000
Stock-based compensation expense	4,847												4,847
Restricted stock units taxes paid in cash	(127)												(127)
Issuance of shares pursuant to conversion notes	21,099						$ 115						20,984
Issuance of shares pursuant to conversion notes (in shares)							11,496,000
Issuance of direct placement — common stock	61,000						$ 102						60,898
Issuance of direct placement — common stock (in shares)							10,167,000
Issuance costs associated with direct placement	(3,310)												(3,310)
Issuance of stock		$ 564						$ 2						$ 562
Issuance of at-the-market placement (in shares)								173,000
Issuance costs associated with at-the-market placement	(17)												(17)
Reclassification of warrant liability to equity	1,893						$ 13						1,880
Reclassification of warrant liability to equity (in shares)							1,293,000
Amortization of shelf fees	(22)												(22)
Cumulative translation (loss) gain	6																		6
Net (loss) income	(117,333)																			(117,333)
Ending Balance at Dec. 31, 2017	(214,732)						$ 1,192						2,638,992						(18)	(2,854,898)
Ending Balance (in shares) at Dec. 31, 2017							119,053,000
Exercise of stock options	$ 7												7
Exercise of stock options (in shares)	6,880						7,000
Issuance of common shares from the release of restricted stock units	$ 1						$ 2						(1)
Issuance of common shares from the release of restricted stock units (in shares)							193,000
Issuance of common shares under Employee Stock Purchase Plan	345						$ 3						342
Issuance of common shares under Employee Stock Purchase Plan (in shares)							400,000
Stock-based compensation expense	6,857												6,857
Issuance of shares pursuant to conversion notes				$ 8,160	$ 38,128	$ 4,980				$ 30	$ 197	$ 27				$ 8,130	$ 37,931	$ 4,953
Issuance of shares pursuant to conversion notes (in shares)										3,000,000	19,726,000	2,726,000
Issuance of direct placement — common stock	28,000						$ 140						27,860
Issuance of direct placement — common stock (in shares)							14,000,000
Issuance costs associated with direct placement	(1,610)												(1,610)
Issuance cost associated with public offering	(2,538)												(2,538)
Issuance of stock		$ 2,089	$ 40,000					$ 10	$ 267					$ 2,079	$ 39,733
Issuance of at-the-market placement (in shares)								1,028,000	26,667,000
Issuance costs associated with at-the-market placement	(84)												(84)
Issuance of shares under Market Price Stock Purchase Plan	430						$ 2						428
Issuance of shares under Market Price Stock Purchase Plan (in shares)							230,000
Amortization of shelf fees	(12)												(12)
Cumulative translation (loss) gain	(1)																		(1)
Adjustment to adopt ASU 2014-09 (Topic 606) | Topic 606	1,873																			1,873
Net (loss) income	(86,975)																			(86,975)
Ending Balance at Dec. 31, 2018	$ (175,082)						$ 1,870						$ 2,763,067						$ (19)	$ (2,940,000)
Ending Balance (in shares) at Dec. 31, 2018							187,030,000