Stock-based Payments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	$ 4.5	$ 11.4	$ 16.7	$ 33.6
Time-Based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	0.1	1.4	0.4	3.9
Unrecognized compensation cost related to non-vested time-based option awards	0.6		0.6
Performance-Based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-IPO stock-based compensation	$ 0.0	$ 2.7	$ 0.0	$ 8.2