EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,073	$ 2,182
Interest cost	2,408	2,278
Expected return on plan assets	(5,319)	(5,224)
Recognized actuarial loss	2,186	2,862
Prior service cost (credit) amortization	25	25
Net periodic benefit cost	1,373	2,123
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1,076	1,211
Interest cost	1,589	1,518
Expected return on plan assets	(1,894)	(1,683)
Recognized actuarial loss	1,421	1,977
Prior service cost (credit) amortization	(36)	(45)
Net periodic benefit cost	$ 2,156	$ 2,978