Summary of Significant Accounting Policies - Warrant liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Beginning balance	$ 1,640	$ 1,697
Change in fair value of warrants	5	(244)
Conversion into common stock warrants	$ (1,645)
Ending balance		1,640
MidCap Credit Facility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Change in fair value of warrants		$ 187