Income Taxes - Reconciliation of Income Taxes/(Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax benefit at U.S. federal statutory rate	$ (5,353)	$ (12,183)
Increase in domestic valuation allowance	10,162	14,236
State income taxes benefit before valuation allowance, net of federal benefit	(1,160)	(1,122)
Warrant revaluation income and other financing costs	(3,742)	(1,026)
Credits	(366)	0
Stock-based compensation	239	292
Return to provision true-ups	220	(40)
Other	0	(157)
Income tax expense (benefit)	$ 0	$ 0