Summary of Significant Accounting Policies - Supplementary cash flows information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Non-cash information:
Warrants exercised for common stock	$ 104	$ 3,538	$ 0
Right-of-use asset and lease liability recognized	2,599	0	0
Additions to equipment in process included in accounts payable	217	606	341
Shares exchanged between common and preferred stock	0	0	(38,389)
Cash information:
Interest paid (net of interest capitalized)	0	2,230	931
Income tax withholding paid	0	0	100
Cash, cash equivalents, and restricted cash	26,978	18,286	$ 26,862	$ 22,978
Cash and cash equivalents	26,889	18,286
Restricted cash	$ 89	$ 0