Schedule of Components of Lease Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost
Amortization of right-of-use assets	$ 0.9	$ 0.9
Interest on lease liabilities	0.1	0.1
Operating lease cost	16.6	16.9
Short-term lease cost	0.8	0.7
Variable lease cost	1.7	1.8
Total lease cost	$ 20.1	$ 20.4