Preferred Stock and Common Stock Warrants - Beneficial Conversion Feature (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allocation of net cash proceeds
Gross proceeds				$ 20,945
Net proceeds - Initial Fair Value Allocation				20,945
Series A convertible preferred stock
Allocation of net cash proceeds
Deemed dividends - accretion of beneficial conversion feature - temporary equity	$ 488	$ 551	$ 0	1,000	$ 0
Series A convertible preferred stock | BCF
Allocation of net cash proceeds
Accretion of stock discount as a deemed dividend				2,500
Series B convertible preferred stock
Allocation of net cash proceeds
Net proceeds - Initial Fair Value Allocation				19,009
Per balance sheet upon issuance				19,009
Series B Warrants
Allocation of net cash proceeds
Net proceeds - Initial Fair Value Allocation				1,936
Per balance sheet upon issuance				$ 1,936