Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Deferred tax assets	$ 67.1	$ 18.0
Amortization period for tax basis intangibles	15 years
Deferred tax liabilities	61.1	48.3
Liability for uncertain tax positions	17.5	17.5
Accrued Interest and penalties associated with uncertain tax positions	5.1	3.9
Expense for interest and penalties related to unrecognized tax benefits	$ 1.4	$ 1.3	$ 1.5
Number of years federal income tax returns are subject to examination	3 years
Period in which significant changes in unrecognized tax benefits are not expected	Next twelve months