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
Lease Cost
Operating lease cost	$ 1.4	$ 2.3	$ 2.6	$ 4.6
Financing lease cost:
Depreciation of lease assets	0.3	0.2	0.7	0.4
Interest on lease liabilities	0.1	0.1	0.1	0.2
Sublease income	(0.7)	(1.1)	(1.3)	(2.1)
Total lease cost, net	$ 1.1	$ 1.5	$ 2.1	$ 3.1