Allowance for Doubtful Accounts - Summary of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Balance at beginning of year	$ 0.9	$ 0.7	$ 0.8
Provision charged to expense	1.2	0.2
Write-offs, less recoveries			(0.1)
Balance at end of year	$ 2.1	$ 0.9	$ 0.7