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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 14.2	$ 12.8	$ 41.0	$ 37.3
Cost of services
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	13.6	11.8	38.8	34.1
Selling, general and administrative
Property, Plant and Equipment [Line Items]
Total depreciation and amortization	$ 0.6	$ 1.0	$ 2.2	$ 3.2