EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Postemployment employee benefit asset
Noncurrent	$ 40,813	$ 24,660
Postemployment employee benefit liability
Noncurrent	(108,830)	(64,609)
Pension
Change in Benefit Obligation
Benefit obligation at beginning of year	333,532	290,321
Service cost	5,523	4,976	$ 5,402
Interest cost	15,433	16,240	15,174
Plan amendments	0	0
Plan participants’ contributions	20	27
Actuarial (gain) loss	(12,216)	36,863
Benefits paid, net of retiree subsidies received	(16,838)	(14,895)
Benefit obligation at end of year	325,454	333,532	290,321
Change in plan assets
Fair value of plan assets at beginning of year	342,710	298,361
Actual return on plan assets	28,156	58,682
Employer contributions	539	535
Reimbursement from Trust	0	0
Benefits paid, net of plan participants’ contributions	(16,819)	(14,868)
Fair value of plan assets at end of year	354,586	342,710	298,361
Funded status	29,132	9,178
Postemployment employee benefit asset
Noncurrent	40,813	21,104
Postemployment employee benefit liability
Current	(555)	(552)
Noncurrent	(11,126)	(11,374)
Total	29,132	9,178
OPEB
Change in Benefit Obligation
Benefit obligation at beginning of year	181,800	203,406
Service cost	1,092	1,406	2,471
Interest cost	8,387	8,327	9,146
Plan amendments	0	(79,881)
Plan participants’ contributions	1,401	703
Actuarial (gain) loss	39,942	54,518
Benefits paid, net of retiree subsidies received	(7,808)	(6,679)
Benefit obligation at end of year	224,814	181,800	203,406
Change in plan assets
Fair value of plan assets at beginning of year	129,721	106,783
Actual return on plan assets	12,063	21,249
Employer contributions	486	7,846
Reimbursement from Trust	(9,139)	0
Benefits paid, net of plan participants’ contributions	(6,538)	(6,157)
Fair value of plan assets at end of year	126,593	129,721	$ 106,783
Funded status	(98,221)	(52,079)
Postemployment employee benefit asset
Noncurrent	0	3,556
Postemployment employee benefit liability
Current	(517)	(2,400)
Noncurrent	(97,704)	(53,235)
Total	$ (98,221)	$ (52,079)