EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,073	$ 2,182	$ 6,219	$ 6,547
Interest cost	2,408	2,278	7,224	6,834
Expected return on plan assets	(5,319)	(5,037)	(15,956)	(15,112)
Recognized actuarial loss	2,186	2,862	6,558	8,585
Prior service cost (credit) amortization	25	25	76	76
Net periodic benefit cost	1,373	2,310	4,121	6,930
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1,077	1,211	3,229	3,633
Interest cost	1,588	1,518	4,766	4,553
Expected return on plan assets	(1,893)	(1,625)	(5,681)	(4,873)
Recognized actuarial loss	1,421	1,978	4,263	5,933
Prior service cost (credit) amortization	(35)	(44)	(107)	(134)
Net periodic benefit cost	$ 2,158	$ 3,038	$ 6,470	$ 9,112