Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Private Placement	At-The-Market Sale Agreement	Common Shares	Common Shares Private Placement	Common Shares At-The-Market Sale Agreement	Additional Paid-in Capital	Additional Paid-in Capital Private Placement	Additional Paid-in Capital At-The-Market Sale Agreement	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2013	$ 69,938			$ 52			$ 497,177			$ (2)	$ (427,289)
Beginning Balance (in shares) at Dec. 31, 2013				51,809,000
Stock-based compensation expense related to equity-classified awards | Equity-classified awards	2,750						2,750
Issuance of common stock to settle liability-classified share awards granted to directors (in shares) | Liability Classified Awards				31,000
Issuance of common stock to settle liability-classified share awards granted to directors | Liability Classified Awards	51						51
Issuance of common stock under employee stock purchase plan (in shares)				139,000
Issuance of common stock under employee stock purchase plan	191			$ 139			191
Issuance of warrants in connection with loans payable	413						413
Issuance of restricted stock awards, net of forfeitures				310,000
Change in unrealized gain (loss) on investments	2									2
Net loss	(52,739)										(52,739)
Ending Balance at Dec. 31, 2014	20,606			$ 52			500,582				(480,028)
Ending Balance (in shares) at Dec. 31, 2014				52,289,000
Stock-based compensation expense related to equity-classified awards | Equity-classified awards	1,132						1,132
Exercise of stock options (in shares)				166,000
Exercise of stock options	241						241
Issuance of common stock to settle liability-classified share awards granted to directors (in shares) | Liability Classified Awards				8,000
Issuance of common stock to settle liability-classified share awards granted to directors | Liability Classified Awards	7						7
Issuance of common stock under employee stock purchase plan (in shares)				7,000
Issuance of common stock under employee stock purchase plan	27						27
Issuance of common stock (in shares)						5,913,000
Issuance of common stock			$ 10,218			$ 6			$ 10,212
Forfeiture of restricted stock awards (in shares)				(201,000)
Change in unrealized gain (loss) on investments	(3)									(3)
Net loss	(15,001)										(15,001)
Ending Balance at Dec. 31, 2015	$ 17,227			$ 58			512,201			(3)	(495,029)
Ending Balance (in shares) at Dec. 31, 2015	58,182,000			58,182,000
Issuance of common stock and warrants in a private placement, excluding to related parties, net (in shares)					17,098,000
Issuance of common stock and warrants in a private placement, excluding to related parties, net		$ 14,846			$ 17			$ 14,829
Issuance of common stock and warrants to related parties (in shares)				544,000
Issuance of common stock and warrants to related parties	$ 525			$ 1			524
Stock-based compensation expense related to equity-classified awards | Equity-classified awards	999						999
Issuance of warrants in connection with a private placement	$ (9,344)						(9,344)
Exercise of stock options (in shares)	38,749			39,000
Exercise of stock options	$ 33						33
Issuance of common stock under employee stock purchase plan	2						2
Issuance of warrants in connection with loans payable	667						667
Change in unrealized gain (loss) on investments	9									9
Net loss	(26,887)										(26,887)
Ending Balance at Dec. 31, 2016	$ (1,923)			$ 76			$ 519,911			$ 6	$ (521,916)
Ending Balance (in shares) at Dec. 31, 2016	75,862,946			75,863,000