Allowance for Doubtful Accounts - Summary of Allowance for Doubtful Accounts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Disclosure [Abstract]
Balance at beginning of year	$ 0.6	$ 0.5	$ 0.7
Provision charged to expense		0.6	0.7
Write-offs, less recoveries		(0.5)	(0.9)
Balance at end of year	$ 0.6	$ 0.6	$ 0.5