Segment Information - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting [Abstract]
Number of reportable segments (in segment) | segment	2
Outside the United States
Segment Reporting Information [Line Items]
Revenues | $	$ 25.5	$ 26.3	$ 37.0