EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,350	$ 2,073	$ 4,051	$ 6,219
Interest cost	3,794	2,408	11,381	7,224
Expected return on plan assets	(4,993)	(5,319)	(14,979)	(15,956)
Recognized actuarial loss	75	2,186	225	6,558
Prior service cost (credit) amortization	25	25	76	76
Net periodic benefit cost	251	1,373	754	4,121
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	618	1,077	1,854	3,229
Interest cost	2,286	1,588	6,859	4,766
Expected return on plan assets	(1,680)	(1,893)	(5,041)	(5,681)
Recognized actuarial loss	0	1,421	0	4,263
Prior service cost (credit) amortization	0	(35)	0	(107)
Net periodic benefit cost	$ 1,224	$ 2,158	$ 3,672	$ 6,470