Income Taxes - Reconciliation of Income Taxes/(Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax benefit at U.S. federal statutory rate	$ (12,183)	$ (8,977)	$ (11,044)
Increase in domestic valuation allowance	14,236	11,109	11,626
State income taxes/(benefit) before valuation allowance, net of federal benefit	(1,122)	(846)	(1,026)
Warrant revaluation and other finance (income)/expense	(1,026)	(1,375)	369
Other	95	89	75
Income tax expense (benefit)	$ 0	$ 0	$ 0