Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Effective income tax rate	28.10%	27.50%	24.30%	25.00%
Unrecognized tax benefits, uncertain tax positions	$ 5.7		$ 5.7		$ 4.6
Unrecognized tax benefits, accrued interest	$ 0.3		$ 0.3		$ 0.2