Revenue From Contracts With Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Jan. 01, 2018
Disaggregation of Revenue [Line Items]
Extended payment terms granted, minimum period to adjust contract consideration for the time value of money		1 year
Contract assets	$ 1.3	$ 1.3
Contract liabilities	31.6	31.6	$ 21.4
Revenue recognized	7.4	10.8
Deferred contract costs	71.2	71.2
Amortization of deferred contract costs	8.5	25.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	118.0	118.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	437.2	437.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	666.5	666.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	$ 1,200.0	$ 1,200.0