Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Income Tax Contingency [Line Items]
Effective tax rate	37.80%	38.60%
Unrecognized tax benefits	$ 1.2		$ 1.3
Unrecognized tax benefits if recognized would reduce effective tax rate in future periods	1.2
Income taxes paid	$ 19.0	$ 14.3