Property, Equipment, and Software - Allocation of Depreciation and Amortization Expense between Cost of Services and Selling, General and Administrative Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 10.6	$ 9.7	$ 29.4	$ 20.9
Cost of services
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	9.2	7.7	26.7	17.5
Selling, general and administrative
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 1.4	$ 2.0	$ 2.7	$ 3.4