Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income tax expense at federal statutory rate, rate	35.00%	35.00%	35.00%	35.00%
Unrecognized income tax benefits	$ 7.8		$ 7.8		$ 7.1
Recognized additional liabilities			$ 0.7	$ 0.7