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, 2020	Sep. 30, 2019	Sep. 30, 2018
Net Periodic Pension Cost in Income Statement
Net Periodic Pension Cost in Income Statement, Interest cost	$ 1,875	$ 2,366	$ 2,279
Net Periodic Pension Cost in Income Statement, Actual return on plan assets	(6,538)	(9,380)	942
Net Periodic Pension Cost in Income Statement, Investment and other expenses	(539)	(483)	(394)
Net Periodic Pension Cost in Income Statement, Difference between actual and expected return on plan assets	4,268	7,086	(3,705)
Net Periodic Pension Cost in Income Statement, Anticipated expenses	334	310	328
Net Periodic Pension Cost in Income Statement, Amortization of unrecognized net actuarial loss	1,617	1,821	1,791
Net Periodic Pension Cost in Income Statement, Annual cost/change	1,017	1,720	1,241
Cash
Cash, Employer contributions/ Annual cost/change			(1,653)
Fair Value of Pension Plan Assets
Fair Value of Pension Plan Assets, Beginning Balance	66,838	61,924	65,676
Fair Value of Pension Plan Assets, Actual return on plan assets	6,538	9,380	(942)
Fair Value of Pension Plan Assets, Employer contributions			1,653
Fair Value of Pension Plan Assets, Benefit payments	(4,288)	(4,466)	(4,463)
Fair Value of Pension Plan Assets, Annual cost/change	2,250	4,914	(3,752)
Fair Value of Pension Plan Assets, Ending Balance	69,088	66,838	61,924
Projected Benefit Obligation
Projected Benefit Obligation, Beginning balance	(65,007)	(59,542)	(65,781)
Projected Benefit Obligation, Interest cost	(1,875)	(2,366)	(2,279)
Projected Benefit Obligation, Benefit payments	4,288	4,466	4,463
Projected Benefit Obligation, Investment and other expenses	539	483	394
Projected Benefit Obligation , Anticipated expenses	(334)	(310)	(328)
Projected Benefit Obligation, Actuarial Loss	(3,009)	(7,738)	3,989
Projected Benefit Obligation, Annual cost/change	(391)	(5,465)	6,239
Projected Benefit Obligation, Ending balance	(65,398)	(65,007)	(59,542)
Funded status at the end of the year	3,690	1,831	2,382
Other Comprehensive (Income) / Loss
Other Comprehensive (Income) / Loss, Difference between actual and expected return on plan assets	(4,268)	(7,086)	3,705
Other Comprehensive (Income) / Loss, Actuarial gain (loss)	3,009	7,738	(3,989)
Other Comprehensive (Income) / Loss, Amortization of unrecognized net actuarial loss	(1,617)	(1,821)	(1,791)
Other Comprehensive (Income) / Loss, Annual cost/change	(2,876)	(1,169)	(2,075)
Gross Pension Related Accumulated Other Comprehensive Income
Gross Pension Related Accumulated Other Comprehensive Income, Beginning Balance	15,104	16,273	18,348
Other Comprehensive (Income) / Loss, Annual cost/change	(2,876)	(1,169)	(2,075)
Gross Pension Related Accumulated Other Comprehensive Income, Ending Balance	$ 12,228	$ 15,104	$ 16,273