Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	At-The-Market Sale Agreement	Common Shares	Common Shares At-The-Market Sale Agreement	Additional Paid-in Capital	Additional Paid-in Capital At-The-Market Sale Agreement	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2012			43,780,000
Beginning Balance at Dec. 31, 2012	$ 118,938		$ 44		$ 439,173		$ (19)	$ (320,260)
Exercise of stock options (in shares)			185,000
Exercise of stock options	272		$ 1		271
Stock-based compensation expense related to equity-classified awards | Equity-classified awards	3,791				3,791
Issuance of common stock to settle liability-classified share awards granted to directors (in shares) | Liability Classified Awards			39,000
Issuance of common stock to settle liability-classified share awards granted to directors | Liability Classified Awards	119				119
Issuance of common stock under employee stock purchase plan (in shares)			110,000
Issuance of common stock under employee stock purchase plan	193				193
Issuance of common stock (in shares) | follow-on stock offering			7,667,000
Issuance of common stock | follow-on stock offering	53,637		$ 7		53,630
Issuance of restricted stock awards, net of forfeitures			28,000
Change in unrealized gain/loss on investments	(9)						(9)
Cumulative translation adjustment	26						26
Net loss	(107,029)							(107,029)
Ending Balance (in shares) at Dec. 31, 2013			51,809,000
Ending Balance at Dec. 31, 2013	69,938		$ 52		497,177		(2)	(427,289)
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				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 (in shares) at Dec. 31, 2014	52,289,000		52,289,000
Ending Balance at Dec. 31, 2014	$ 20,606		$ 52		500,582			(480,028)
Exercise of stock options (in shares)	165,805		166,000
Exercise of stock options	$ 241				241
Stock-based compensation expense related to equity-classified awards	1,132				1,132
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 (in shares) at Dec. 31, 2015	58,181,715		58,181,715
Ending Balance at Dec. 31, 2015	$ 17,227		$ 58		$ 512,201		$ (3)	$ (495,029)