Income Taxes - Schedule of Unrecognized Tax Benefit (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Beginning balance	$ 30.5	$ 29.6	$ 26.9
Increases in tax positions for prior years	13.9	2.8	0.3
Decreases in tax positions for prior years	(0.1)	(2.9)	(1.0)
Purchase Accounting			0.3
Increases in tax positions for current year	4.4	4.6	4.0
Settlements	(1.1)	(0.3)	(0.2)
Lapse in statutes of limitation	(1.3)	(3.3)	(0.7)
Ending balance	$ 46.3	$ 30.5	$ 29.6