Share-Based Compensation - Allocated Share-based Compensation Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	$ 14.1	$ 18.8	$ 6.1
Cost of Revenue
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	2.7	2.2	2.3
Selling, General and Administrative Expenses
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	6.2	3.4	3.8
Restructuring and Related Charges
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	0.8
Continuing Operations
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	9.7	5.6	6.1
Total income tax benefit recognized in continuing operations	2.5	1.4	$ 1.6
Discontinued Operations
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation costs	$ 4.4	$ 13.2