Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]
Eligible employees contribution to 401(k) plan (up to 25%)	25.00%
Employer contributions into 401(k) plans	$ 7.3	$ 7.1	$ 6.3
Employee incentive plans expenses	$ 40.0	$ 20.3	$ 25.0