Assets and Liabilities Measured at Fair Value - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended								12 Months Ended
	Jul. 31, 2015 USD ($) shares	Feb. 28, 2015 USD ($) shares	Oct. 31, 2013 USD ($) shares	May. 31, 2012 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) shares	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Input $ / shares shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares	Apr. 30, 2014 $ / shares	Dec. 31, 2012 $ / shares shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of inputs used for valuation of warrants | Input													6
Sale of units to underwriter	9,400,000
Common stock sold through the program (in shares)	9,400,000	2,500,000	1,300,000	1,000,000											0
Proceeds From Issuance Of Common Stock | $	$ 6,000
Exercise price of Warrants (in dollars per share) | $ / shares																	$ 19.20
Warrant outstanding					18,059,000				850,138				18,059,000	850,138	929,495		352,664
Proceeds from issuance of private placement | $		$ 2,600	$ 7,500	$ 21,500
Net proceeds from issuance of private placement | $		2,500	6,900	21,100
Derivative warrant liability [Abstract]
Change in fair value of the warrant liability, net | $					$ 850	$ (1,253)	$ 48	$ (209)	$ (330)	$ (519)	$ (1,297)	$ 205	$ 564	$ 1,942	$ 2,756
Derivative warrant liabilities | $					$ 3,785				$ 225				$ 3,785	$ 225
February 2015 Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Value of warrants issued | $		$ 800
Exercise price of Warrants (in dollars per share) | $ / shares					$ 0.74								$ 0.74
Warrant outstanding					1,100,000								1,100,000
Number of warrants exercised													0
Warrants issued (in shares)		1,100,000
Proceeds from issuance of private placement | $		$ 2,600
Net proceeds from issuance of private placement | $		$ 2,500
Term period for warrants													5 years
Series A Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Term period for warrants													5 years
2013 Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Value of warrants issued | $			$ 1,900
Exercise price of Warrants (in dollars per share) | $ / shares					$ 7.04								$ 7.04			$ 7.04
Warrant outstanding					600,000								600,000
Number of warrants exercised													0
Warrants issued (in shares)			600,000
Term period for warrants													5 years
2012 Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Value of warrants issued | $				$ 3,400
Warrants expiration date													May 31, 2015
Warrants issued (in shares)				300,000
Term period for warrants													3 years
Warrants Exercised (in shares)													200,000
Net proceeds from exercise of warrants | $													$ 200
Series A Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of warrants converted	7,000,000
Gross Proceeds From Underwriting Offering | $	$ 7,000
Exercise price of Warrants (in dollars per share) | $ / shares					$ 0.87								$ 0.87
Warrant outstanding					7,000,000								7,000,000
Warrants expiry period													5 years
Series B Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of warrants converted	9,400,000
Exercise price of Warrants (in dollars per share) | $ / shares					$ 0.75								$ 0.75
Warrant outstanding					9,400,000								9,400,000
Warrants expiration date													Jan. 29, 2016
Series A and B Common Stock Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Value of warrants issued | $	$ 3,400
Number of warrants exercised													0