Severance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance expense	$ 0.3	$ 3.2
Severance
Restructuring Cost and Reserve [Line Items]
Severance liability	0.2
Current severance liability	$ 0.1