EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2024	Jan. 02, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Postemployment employee (liability)
Noncurrent	$ (42,333)			$ (42,333)		$ (102,528)
OPEB
Change in Benefit Obligation
Benefit obligation at beginning of period		$ 203,406		203,406	$ 173,217	173,217
Service cost	255	642	$ 618	897	1,236	2,471
Interest cost	$ 1,808	2,902	$ 2,287	4,710	4,573	9,146
Plan amendments		(81,283)				0
Plan participants’ contributions		0				552
Actuarial loss		26,871				25,363
Benefits paid, net of retiree subsidies received		(1,614)				(7,343)
Benefit obligation at end of period		150,924				203,406
Change in plan assets
Fair value of plan assets at beginning of period		106,783		$ 106,783	$ 99,736	99,736
Actual return on plan assets		8,995				9,826
Employer contributions		3,181				4,192
Benefits paid, net of plan participants’ contributions		(1,612)				(6,971)
Fair value of plan assets at end of period		117,347				106,783
Funded status		(33,577)				(96,623)
Postemployment employee (liability)
Current		(1,613)				(4,201)
Noncurrent		(31,964)				(92,422)
Total		$ (33,577)				$ (96,623)