Leases - Components of Lease Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Leases [Abstract]
Operating Lease Cost	$ 2.9	$ 3.1	$ 5.9	$ 6.3
Finance Lease Cost:
Amortization of right-of-use assets	0.3	0.3	0.7	0.6
Interest on lease liabilities	0.1	0.1	0.1	0.1
Total finance lease cost	$ 0.4	$ 0.4	$ 0.8	$ 0.7