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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 9.4	$ 6.3	$ 18.8	$ 11.2
Cost of services
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	8.6	5.2	17.5	9.8
Selling, general and administrative
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 0.8	$ 1.1	$ 1.3	$ 1.4