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, 2021	Sep. 30, 2020	Sep. 30, 2019
Net Periodic Pension Cost in Income Statement
Net Periodic Pension Cost in Income Statement, Interest cost	$ 1,541	$ 1,875	$ 2,366
Net Periodic Pension Cost in Income Statement, Actual return on plan assets	(678)	(6,538)	(9,380)
Net Periodic Pension Cost in Income Statement, Investment and other expenses	(377)	(539)	(483)
Net Periodic Pension Cost in Income Statement, Difference between actual and expected return on plan assets	(1,386)	4,268	7,086
Net Periodic Pension Cost in Income Statement, Anticipated expenses	345	334	310
Net Periodic Pension Cost in Income Statement, Amortization of unrecognized net actuarial loss	937	1,617	1,821
Net Periodic Pension Cost in Income Statement, Annual cost/change	382	1,017	1,720
Fair Value of Pension Plan Assets
Fair Value of Pension Plan Assets, Beginning Balance	69,088	66,838	61,924
Fair Value of Pension Plan Assets, Actual return on plan assets	678	6,538	9,380
Fair Value of Pension Plan Assets, Benefit payments	(4,429)	(4,288)	(4,466)
Fair Value of Pension Plan Assets, Annual cost/change	(3,751)	2,250	4,914
Fair Value of Pension Plan Assets, Ending Balance	65,337	69,088	66,838
Projected Benefit Obligation
Projected Benefit Obligation, Beginning balance	(65,398)	(65,007)	(59,542)
Projected Benefit Obligation, Interest cost	(1,541)	(1,875)	(2,366)
Projected Benefit Obligation, Benefit payments	4,429	4,288	4,466
Projected Benefit Obligation, Investment and other expenses	377	539	483
Projected Benefit Obligation , Anticipated expenses	(345)	(334)	(310)
Projected Benefit Obligation, Actuarial loss (gain)	1,184	(3,009)	(7,738)
Projected Benefit Obligation, Annual cost/change	4,104	(391)	(5,465)
Projected Benefit Obligation, Ending balance	(61,294)	(65,398)	(65,007)
Funded status at the end of the year	4,043	3,690	1,831
Other Comprehensive (Income) / Loss
Other Comprehensive (Income) / Loss, Difference between actual and expected return on plan assets	1,386	(4,268)	(7,086)
Other Comprehensive (Income) / Loss, Actuarial loss (gain)	(1,184)	3,009	7,738
Other Comprehensive (Income) / Loss, Amortization of unrecognized net actuarial loss	(937)	(1,617)	(1,821)
Other Comprehensive (Income) / Loss, Annual cost/change	(735)	(2,876)	(1,169)
Gross Pension Related Accumulated Other Comprehensive Income
Gross Pension Related Accumulated Other Comprehensive Income, Beginning Balance	12,228	15,104	16,273
Other Comprehensive (Income) / Loss, Annual cost/change	(735)	(2,876)	(1,169)
Gross Pension Related Accumulated Other Comprehensive Income, Ending Balance	$ 11,493	$ 12,228	$ 15,104