Debt and Related Warrants - Carrying Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt
Net carrying value of debt, Current Portion	$ 3,987	$ 3,884
Net carrying value of debt, Long-term debt	8,178	4,218
2017 Credit Facility
Debt
Debt, including end of term fee, Current Portion	4,000
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Current Portion	(23)
Net carrying value of debt, Current Portion	3,977
Debt, including end of term fee, Long-term debt	8,720
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Long-term debt	(563)
Net carrying value of debt, Long-term debt	8,157
Debt, including end of term fee, Total	12,720
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Total	(586)
Net carrying value of debt, Total	$ 12,134
2015 Credit Facility
Debt
Debt, including end of term fee, Current Portion		4,054
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Current Portion		(177)
Net carrying value of debt, Current Portion		3,877
Debt, including end of term fee, Long-term debt		4,301
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Long-term debt		(83)
Net carrying value of debt, Long-term debt		4,218
Debt, including end of term fee, Total		8,355
Less: Discount attributable to warrants, end of term fee and debt issuance costs, Total		(260)
Net carrying value of debt, Total		$ 8,095