Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Income Tax Contingency [Line Items]
Effective tax rate	38.10%	39.50%
Unrecognized tax benefits	$ 1.6		$ 1.3
Unrecognized tax benefits if recognized would reduce effective tax rate in future periods	1.6
Income taxes paid	$ 28.1	$ 21.1