Leases - Lease expense (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease cost:
Operating lease cost(1)	[1]	$ 7.2	$ 5.9	$ 22.1	$ 16.6
Short-term lease		1.4	1.1	3.7	3.4
Total lease cost		$ 8.6	$ 7.0	$ 25.8	$ 20.0

[1] Operating lease cost includes an immaterial amount of variable expenses and sublease rental income