Leases - Components of Lease Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating Lease Cost	$ 3.1	$ 3.0	$ 6.3	$ 6.2
Finance Lease Cost:
Amortization of right-of-use assets	0.3	0.4	0.6	0.9
Interest on lease liabilities	0.1	0.1	0.1	0.1
Total finance lease cost	$ 0.4	$ 0.5	$ 0.7	$ 1.0