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, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Net Periodic Pension Cost in Income Statement
Net Periodic Pension Cost in Income Statement, Interest cost	$ 1,968	$ 2,133	$ 2,312
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Income (Expense), Operating and Nonoperating	Interest Income (Expense), Operating and Nonoperating	Interest Income (Expense), Operating and Nonoperating
Net Periodic Pension Cost in Income Statement, Actual return on plan assets	$ (1,009)	$ (6,672)	$ (1,196)
Net Periodic Pension Cost in Income Statement, Difference between actual and expected return on plan assets	(759)	4,558	(635)
Net Periodic Pension Cost in Income Statement, Amortization of unrecognized net actuarial loss	1,728	1,277	1,526
Net Periodic Pension Cost in Income Statement, Annual cost/change	1,928	1,296	2,007
Cash
Cash, Employer contributions/ Annual cost/change			(64)
Fair Value of Pension Plan Assets
Fair Value of Pension Plan Assets, Beginning Balance	46,990	44,206	47,454
Fair Value of Pension Plan Assets, Actual return on plan assets	1,009	6,672	1,196
Fair Value of Pension Plan Assets, Employer contributions			64
Fair Value of Pension Plan Assets, Benefit payments	(3,969)	(3,649)	(3,936)
Fair Value of Pension Plan Assets, Investment and other expenses	(485)	(239)	(572)
Fair Value of Pension Plan Assets, Annual cost/change	(3,445)	2,784	(3,248)
Fair Value of Pension Plan Assets, Ending Balance	43,545	46,990	44,206
Projected Benefit Obligation
Projected Benefit Obligation, Beginning balance	(44,274)	(41,485)	(44,253)
Projected Benefit Obligation, Interest cost	(1,968)	(2,133)	(2,312)
Projected Benefit Obligation, Benefit payments	3,969	3,649	3,936
Projected Benefit Obligation, Investment and other expenses	485	239	572
Projected Benefit Obligation, Actuarial (loss) gain	499	(4,544)	572
Projected Benefit Obligation, Annual cost/change	2,985	(2,789)	2,768
Projected Benefit Obligation, Ending balance	(41,289)	(44,274)	(41,485)
Funded status at the end of the year	2,256	2,716	2,721	$ 3,201
Other Comprehensive (Income) / Loss
Other Comprehensive (Income) / Loss, Difference between actual and expected return on plan assets	759	(4,558)	635
Other Comprehensive (Income) / Loss, Actuarial loss (gain)	(499)	4,544	(572)
Other Comprehensive (Income) / Loss, Amortization of unrecognized net actuarial loss	(1,728)	(1,277)	(1,526)
Other Comprehensive (Income) / Loss, Annual cost/change	(1,468)	(1,291)	(1,463)
Gross Pension Related Accumulated Other Comprehensive Income
Gross Pension Related Accumulated Other Comprehensive Income, Beginning Balance	9,174	10,465	11,928
Other Comprehensive (Income) / Loss, Annual cost/change	(1,468)	(1,291)	(1,463)
Gross Pension Related Accumulated Other Comprehensive Income, Ending Balance	$ 7,706	$ 9,174	$ 10,465