Employee Benefit Plans - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Employee benefits costs	$ 264,193	$ 191,947	$ 162,495
Discretionary Contributions
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	100.00%
Employee Contributions upto 3%
Defined Benefit Plan Disclosure [Line Items]
Percentage of compensation	3.00%
50% Percentage of Matching Contribution
Defined Benefit Plan Disclosure [Line Items]
Discretionary match percentage	50.00%
Employee Contribution Next 2%
Defined Benefit Plan Disclosure [Line Items]
Percentage of compensation	2.00%