Summary of Significant Accounting Policies - Summary of Self-Insured Liabilities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Insurance Risks [Line Items]
Self-insured liabilities at beginning of year	$ 7.4	$ 7.9
Expense	2.4	2.1
Reversal of self-insured liabilities	(1.0)	(1.0)
Cash expenditures	(1.2)	(1.6)
Self-insured liabilities at end of year	$ 7.6	$ 7.4