EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,380	$ 1,244	$ 2,761	$ 2,488
Interest cost	3,859	4,060	7,717	8,120
Expected return on plan assets	(5,925)	(5,086)	(11,850)	(10,173)
Recognized actuarial loss	300	30	601	59
Prior service cost (credit) amortization	0	15	0	31
Net periodic benefit (credit) cost	(386)	263	(771)	525
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	273	255	546	897
Interest cost	2,097	1,808	4,194	4,710
Expected return on plan assets	(2,347)	(2,020)	(4,693)	(3,878)
Recognized actuarial loss	1,793	1,255	3,586	1,751
Prior service cost (credit) amortization	(3,270)	(3,337)	(6,540)	(3,337)
Net periodic benefit (credit) cost	$ (1,454)	$ (2,039)	$ (2,907)	$ 143