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, 2013	Sep. 30, 2012	Sep. 30, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets, end of year	$ 65,295	$ 52,249
Pension Plans
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	3,326	2,653	2,432
Interest cost	3,944	3,914	3,541
Pension Plans | Change in Benefit Obligation
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation, beginning of year	96,989	73,383
Service cost	3,326	2,653
Interest cost	3,944	3,915
Amendments	298
Actuarial losses	(18,090)	18,693
Benefits paid	(1,781)	(1,655)
Benefit obligation, end of year	84,686	96,989
Pension Plans | Change in Plan Assets
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets, beginning of year	52,249	36,935
Actual return (loss) on plan assets	8,124	7,649
Employer contributions	6,704	9,320
Benefits paid	(1,781)	(1,655)
Fair value of plan assets, end of year	65,296	52,249
Funded status	(19,390)	(44,740)
SERP
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	817	435	324
Interest cost	422	369	356
SERP | Change in Benefit Obligation
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation, beginning of year	11,087	7,942
Service cost	817	435
Interest cost	422	369
Actuarial losses	(615)	2,868
Benefits paid	(525)	(527)
Benefit obligation, end of year	11,186	11,087
SERP | Change in Plan Assets
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Employer contributions	525	527
Benefits paid	(525)	(527)
Funded status	$ (11,186)	$ (11,087)