Fair Value - Schedule of Changes in Estimated Fair Value for Level 3 Classified Derivative Warrant Liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair value at the beginning of period	$ 261	$ 11,538
Change in fair value	20	(1,850)
Exchange / conversion to common shares		(9,688)
Fair value at the end of period	$ 203
2017 Series F Preferred Stock Warrant Liability [Member]
Fair value at the beginning of period		3,388
Change in fair value		(863)
Exchange / conversion to common shares		(2,525)
Fair value at the end of period
2017 Series F Preferred Stock Embedded Derivative [Member]
Fair value at the beginning of period		8,150
Change in fair value		(987)
Exchange / conversion to common shares		(7,163)
Fair value at the end of period