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Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit	$ (2,200.8)		$ (2,225.7)
Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognized from deferred revenue	22.8
Contract asset reclassified to receivables	$ 4.0
Revenue, practical expedient, incremental cost of obtaining contract	true
Revenue, remaining performance obligation, optional exemption, performance obligation	true
Cumulative Impact of Adopting Topic 606 \| Accounting Standards Update 2014-09
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit		$ 12.9