Basis of Presentation - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Basis of Presentation [Abstract]
Warrants exercised for common stock	$ 0	$ 2,409
Interest paid (net of interest capitalized)	4	754
Additions to equipment in process included in accounts payable	365	459
Right-of-use asset and lease liability recognized	$ 560	$ 0