Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 3.5	$ 3.4	$ 10.2	$ 8.9
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0.4	0.7	1.5	2.0
Time-based restricted share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	2.5	1.8	6.8	4.2
Performance-based restricted share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0.5	0.8	1.7	2.5
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 0.1	$ 0.1	$ 0.2	$ 0.2