Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 1.8	$ 5.2	$ 4.1
Additions Acquisition Beginning Balance		0.2
Additions Charged to Costs and Expenses	0.1	(0.7)	1.4
Deductions & Write-offs	0.1	(2.9)	(0.3)
Balance at End of Year	2.0	1.8	5.2
Valuation Allowance for Sales Returns [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	1.4	1.0	1.3
Additions Charged to Costs and Expenses	0.3	0.2	0.1
Deductions & Write-offs	0.1	0.2	(0.4)
Balance at End of Year	1.8	1.4	1.0
Valuation Allowance on Deferred Tax Asset [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	27.4	17.9	13.6
Additions Acquisition Beginning Balance		5.9
Additions Charged to Costs and Expenses	4.2	4.9	4.8
Deductions & Write-offs	(1.0)	(1.3)	(0.5)
Balance at End of Year	$ 30.6	$ 27.4	$ 17.9