Net Periodic Benefit Cost for Period Reconciliation of Changes in Plan Assets Projected Benefit Obligations and Amounts Recognized in Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) - Frozen Defined Benefit Pension Plans - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Net Periodic Pension Cost in Income Statement
Net Periodic Pension Cost in Income Statement, Interest cost	$ 2,312	$ 1,560	$ 1,541
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Revenue (Expense), Net	Interest Revenue (Expense), Net	Interest Revenue (Expense), Net
Net Periodic Pension Cost in Income Statement, Actual return on plan assets	$ (1,196)	$ 13,151	$ (1,055)
Net Periodic Pension Cost in Income Statement, Difference between actual and expected return on plan assets	(635)	(15,200)	(1,386)
Net Periodic Pension Cost in Income Statement, Anticipated expenses			345
Net Periodic Pension Cost in Income Statement, Amortization of unrecognized net actuarial loss	1,526	896	937
Net Periodic Pension Cost in Income Statement, Annual cost/change	2,007	407	382
Cash
Cash, Employer contributions/ Annual cost/change	(64)
Fair Value of Pension Plan Assets
Fair Value of Pension Plan Assets, Beginning Balance	47,454	65,337	69,088
Fair Value of Pension Plan Assets, Actual return on plan assets	1,196	(13,151)	1,055
Fair Value of Pension Plan Assets, Employer contributions	64
Fair Value of Pension Plan Assets, Benefit payments	(3,936)	(4,225)	(4,429)
Fair Value of Pension Plan Assets, Investment and other expenses	(572)	(507)	(377)
Fair Value of Pension Plan Assets, Annual cost/change	(3,248)	(17,883)	(3,751)
Fair Value of Pension Plan Assets, Ending Balance	44,206	47,454	65,337
Projected Benefit Obligation
Projected Benefit Obligation, Beginning balance	(44,253)	(61,294)	(65,398)
Projected Benefit Obligation, Interest cost	(2,312)	(1,560)	(1,541)
Projected Benefit Obligation, Benefit payments	3,936	4,225	4,429
Projected Benefit Obligation, Investment and other expenses	572	507	377
Projected Benefit Obligation , Anticipated expenses			(345)
Projected Benefit Obligation, Actuarial (loss) gain	572	13,869	1,184
Projected Benefit Obligation, Annual cost/change	2,768	17,041	4,104
Projected Benefit Obligation, Ending balance	(41,485)	(44,253)	(61,294)
Funded status at the end of the year	2,721	3,201	4,043	$ 3,690
Other Comprehensive (Income) / Loss
Other Comprehensive (Income) / Loss, Difference between actual and expected return on plan assets	635	15,200	1,386
Other Comprehensive (Income) / Loss, Actuarial loss (gain)	(572)	(13,869)	(1,184)
Other Comprehensive (Income) / Loss, Amortization of unrecognized net actuarial loss	(1,526)	(896)	(937)
Other Comprehensive (Income) / Loss, Annual cost/change	(1,463)	435	(735)
Gross Pension Related Accumulated Other Comprehensive Income
Gross Pension Related Accumulated Other Comprehensive Income, Beginning Balance	11,928	11,493	12,228
Other Comprehensive (Income) / Loss, Annual cost/change	(1,463)	435	(735)
Gross Pension Related Accumulated Other Comprehensive Income, Ending Balance	$ 10,465	$ 11,928	$ 11,493