Revenue From Contracts With Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 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	$ 0.7	$ 0.7
Contract liabilities	34.6	34.6	$ 21.4
Revenue recognized	8.7	10.0
Deferred contract costs	78.4	78.4
Amortization of deferred contract costs	8.2	17.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	268.6	268.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	439.6	439.6
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	663.4	663.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Disaggregation of Revenue [Line Items]
Unsatisfied performance obligations	$ 1,400.0	$ 1,400.0

Minimum Period Of Contract To Adjust Contract Consideration For The Time Value Of Money

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Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

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