Leases - Components of Lease Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating Lease Cost	$ 3.0	$ 3.0	$ 9.3	$ 9.3
Finance Lease Cost:
Amortization of right-of-use assets	0.3	0.5	1.0	1.4
Interest on lease liabilities		0.1	0.1	0.2
Total finance lease cost	$ 0.3	$ 0.6	$ 1.1	$ 1.6