Revenues - Performance Obligation (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	$ 720.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	$ 711.1
Revenue, remaining performance obligation, percent	98.70%
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 years