Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Sep. 30, 2012
Income Taxes [Line Items]
Effective income tax rate	31.40%	31.40%	30.90%	31.70%
Unrecognized tax benefits, uncertain tax positions	$ 8.8		$ 8.8		$ 7.5
Unrecognized tax benefits, accrued interest	$ 0.9		$ 0.9		$ 0.7