Schedule of Net Periodic Benefit Cost and Weighted Average Assumptions (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,326	$ 2,653	$ 2,432
Interest cost	3,944	3,914	3,541
Expected return on plan assets	(4,399)	(3,398)	(2,886)
Recognized actuarial losses	3,589	2,549	1,752
Amortization of prior service costs	70	63	63
Net periodic pension cost	6,530	5,781	4,902
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost	817	435	324
Interest cost	422	369	356
Recognized actuarial losses	376
Amortization of prior service costs	420	420	420
Net periodic pension cost	$ 2,035	$ 1,224	$ 1,100