EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Postemployment employee benefit asset
Postemployment employee benefit assets	$ 18,684	$ 4,388
Postemployment employee benefit liability
Noncurrent	(102,528)	(82,867)
Pension
Change in Benefit Obligation
Benefit obligation at beginning of year	290,823	395,547
Service cost	5,402	8,291	$ 8,730
Interest cost	15,174	9,632	9,112
Plan participants’ contributions	32	59
Actuarial (gain) loss	(7,057)	(109,320)
Benefits paid, net of retiree subsidies received	(14,053)	(13,386)
Benefit obligation at end of year	290,321	290,823	395,547
Change in plan assets
Fair value of plan assets at beginning of year	284,347	355,284
Actual return (loss) on plan assets	27,456	(58,239)
Employer contributions	579	628
Benefits paid, net of plan participants’ contributions	(14,021)	(13,326)
Fair value of plan assets at end of year	298,361	284,347	355,284
Funded status	8,040	(6,476)
Postemployment employee benefit asset
Postemployment employee benefit assets	18,684	4,388
Postemployment employee benefit liability
Current	(538)	(578)
Noncurrent	(10,106)	(10,286)
Total	8,040	(6,476)
OPEB
Change in Benefit Obligation
Benefit obligation at beginning of year	173,217	244,674
Service cost	2,471	4,305	4,844
Interest cost	9,146	6,355	6,071
Plan participants’ contributions	552	423
Actuarial (gain) loss	25,363	(77,775)
Benefits paid, net of retiree subsidies received	(7,343)	(4,765)
Benefit obligation at end of year	203,406	173,217	244,674
Change in plan assets
Fair value of plan assets at beginning of year	99,736	114,183
Actual return (loss) on plan assets	9,826	(15,996)
Employer contributions	4,192	6,082
Benefits paid, net of plan participants’ contributions	(6,971)	(4,533)
Fair value of plan assets at end of year	106,783	99,736	$ 114,183
Funded status	(96,623)	(73,481)
Postemployment employee benefit asset
Postemployment employee benefit assets	0	0
Postemployment employee benefit liability
Current	(4,201)	(900)
Noncurrent	(92,422)	(72,581)
Total	$ (96,623)	$ (73,481)