Employee Benefit Plans - Annual Changes in Benefit Obligations and Plan Assets and Funded Status of Pension Plans and SERP (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Pension Plans [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 2,653	$ 2,432	$ 2,196
Interest cost	3,914	3,541	3,281
Pension Plans [Member] | Change In Benefit Obligation [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation, beginning of year	73,383	63,152
Service cost	2,653	2,432
Interest cost	3,915	3,541
Amendments
Actuarial losses	18,693	5,759
Benefits paid	(1,655)	(1,501)
Benefit obligation, end of year	96,989	73,383
Pension Plans [Member] | Change In Plan Assets [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefits paid	(1,655)	(1,501)
Fair value of plan assets, beginning of year	36,935	33,147
Actual return (loss) on plan assets	7,649	(534)
Employer contributions	9,320	5,823
Fair value of plan assets, end of year	52,249	36,935
Funded status	(44,740)	(36,448)
Supplemental Employee Retirement Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	435	324	439
Interest cost	369	356	374
Supplemental Employee Retirement Plan [Member] | Change In Benefit Obligation [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation, beginning of year	7,942	7,683
Service cost	435	324
Interest cost	369	356
Amendments
Actuarial losses	2,868	106
Benefits paid	(527)	(527)
Benefit obligation, end of year	11,087	7,942
Supplemental Employee Retirement Plan [Member] | Change In Plan Assets [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefits paid	(527)	(527)
Employer contributions	527	527
Funded status	$ (11,087)	$ (7,942)