Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income Tax Contingency [Line Items]
Effective tax rate	42.60%	37.80%
Unrecognized tax benefits	$ 2.0		$ 1.3
Unrecognized tax benefits if recognized would reduce effective tax rate in future periods	2
Income taxes paid	$ 21.7	$ 19.0