Fair Value Measurements - Fair Value Hierarchy (Details) - Recurring - Measured at fair value - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents, money market funds with less than 90 days maturity	$ 12,369	$ 12,290
Total Assets	12,369	12,290
Liabilities
Warrant liability	144	152
Derivative liability	2,557	1,474
Total Liabilities	2,701	1,626
Quoted prices in active markets (Level 1)
Assets
Cash and cash equivalents, money market funds with less than 90 days maturity	12,369	12,290
Total Assets	12,369	12,290
Liabilities
Warrant liability	0	0
Derivative liability	0	0
Total Liabilities	0	0
Quoted prices in inactive markets (Level 2)
Assets
Cash and cash equivalents, money market funds with less than 90 days maturity	0	0
Total Assets	0	0
Liabilities
Warrant liability	0	0
Derivative liability	0	0
Total Liabilities	0	0
Significant unobservable inputs (Level 3)
Assets
Cash and cash equivalents, money market funds with less than 90 days maturity	0	0
Total Assets	0	0
Liabilities
Warrant liability	144	152
Derivative liability	2,557	1,474
Total Liabilities	$ 2,701	$ 1,626