Allowance for Doubtful Accounts - Summary of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Balance at beginning of year	$ 3.1	$ 2.1	$ 0.9
Provision charged to expense	0.3	1.1	1.2
Write-offs, less recoveries	(0.4)	(0.1)
Balance at end of year	$ 3.0	$ 3.1	$ 2.1