Derivative Warrants - Warrants Outstanding Reconciliation (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Increase (Decrease) in Temporary Equity [Roll Forward]
Issued	$ 0		$ 0
Warrant
Increase (Decrease) in Temporary Equity [Roll Forward]
Outstanding at the beginning of the period	118	118	118
Issued	$ 0	$ 0
Exercised	$ 0	$ 0
Outstanding at the end of the period	118	118	118