EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Postemployment employee benefit asset
Noncurrent	$ 24,660	$ 18,684
Postemployment employee benefit liability
Noncurrent	(64,609)	(102,528)
Pension
Change in Benefit Obligation
Benefit obligation at beginning of year	290,321	290,823
Service cost	4,976	5,402	$ 8,291
Interest cost	16,240	15,174	9,632
Plan amendments	0	0
Plan participants’ contributions	27	32
Actuarial loss (gain)	36,863	(7,057)
Benefits paid, net of retiree subsidies received	(14,895)	(14,053)
Benefit obligation at end of year	333,532	290,321	290,823
Change in plan assets
Fair value of plan assets at beginning of year	298,361	284,347
Actual return on plan assets	58,682	27,456
Employer contributions	535	579
Benefits paid, net of plan participants’ contributions	(14,868)	(14,021)
Fair value of plan assets at end of year	342,710	298,361	284,347
Funded status	9,178	8,040
Postemployment employee benefit asset
Noncurrent	21,104	18,684
Postemployment employee benefit liability
Current	(552)	(538)
Noncurrent	(11,374)	(10,106)
Total	9,178	8,040
OPEB
Change in Benefit Obligation
Benefit obligation at beginning of year	203,406	173,217
Service cost	1,406	2,471	4,305
Interest cost	8,327	9,146	6,355
Plan amendments	(79,881)	0
Plan participants’ contributions	703	552
Actuarial loss (gain)	54,518	25,363
Benefits paid, net of retiree subsidies received	(6,679)	(7,343)
Benefit obligation at end of year	181,800	203,406	173,217
Change in plan assets
Fair value of plan assets at beginning of year	106,783	99,736
Actual return on plan assets	21,249	9,826
Employer contributions	7,846	4,192
Benefits paid, net of plan participants’ contributions	(6,157)	(6,971)
Fair value of plan assets at end of year	129,721	106,783	$ 99,736
Funded status	(52,079)	(96,623)
Postemployment employee benefit asset
Noncurrent	3,556	0
Postemployment employee benefit liability
Current	(2,400)	(4,201)
Noncurrent	(53,235)	(92,422)
Total	$ (52,079)	$ (96,623)