EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5,523	$ 4,976	$ 5,402
Interest cost	15,433	16,240	15,174
Expected return on plan assets	(23,700)	(20,346)	(19,972)
Recognized actuarial loss	1,203	117	300
Prior service cost (credit) amortization	0	61	103
Net periodic benefit cost recognized as expense	(1,541)	1,048	1,007
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1,092	1,406	2,471
Interest cost	8,387	8,327	9,146
Expected return on plan assets	(9,385)	(7,920)	(6,721)
Recognized actuarial loss	7,171	4,262	0
Prior service cost (credit) amortization	(13,080)	(10,013)	0
Net periodic benefit cost recognized as expense	$ (5,815)	$ (3,938)	$ 4,896