Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012
Income Tax [Line Items]
Effective income tax rate	22.00%	27.00%
Reduction in income tax provision			$ 3.7
Unrecognized tax benefits related to federal, state and foreign taxes	48.5		48.5	43.4
Unrecognized tax benefits that would impact effective tax rate	40.4		40.4
Accrued interest	6.3		6.3	4.8
Decrease in unrecognized tax benefits	$ 18.4		$ 18.4
Number of months unrecognized tax benefits may decrease			12 months