EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,073	$ 2,183	$ 4,146	$ 4,365
Interest cost	2,408	2,278	4,816	4,556
Expected return on plan assets	(5,318)	(4,851)	(10,637)	(10,075)
Recognized actuarial loss	2,186	2,861	4,372	5,723
Prior service cost (credit) amortization	26	26	51	51
Net periodic benefit cost	1,375	2,497	2,748	4,620
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1,076	1,211	2,152	2,422
Interest cost	1,589	1,517	3,178	3,035
Expected return on plan assets	(1,894)	(1,565)	(3,788)	(3,248)
Recognized actuarial loss	1,421	1,978	2,842	3,955
Prior service cost (credit) amortization	(36)	(45)	(72)	(90)
Net periodic benefit cost	$ 2,156	$ 3,096	$ 4,312	$ 6,074