Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Deferred contract costs and capitalized sales commissions
Capitalized Contract Cost [Line Items]
Capitalized contract cost, gross	$ 84.4		$ 84.4		$ 89.2
Capitalized sales commissions to selling, general and administrative expenses
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization	3.0	$ 2.9	6.0	$ 5.5
Other deferred contract costs as a reduction of revenue
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization	$ 1.5	$ 1.4	$ 3.0	$ 2.8