POSTRETIREMENT BENEFITS - Change in Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Change in benefit obligations:
Beginning balance, benefit obligations	$ 103,189	$ 95,330
Interest cost	4,556	5,264	$ 5,175
Actuarial gain (loss)	(3,432)	8,979
Benefits and administrative expenses paid	(6,559)	(6,384)
Ending balance, benefit obligations	97,754	103,189	95,330
Change in plan assets:
Beginning balance, fair value of plan assets	111,934	105,443
Actual return on plan assets	677	12,599
Employer contributions	280	276
Benefits and administrative expenses paid	(6,558)	(6,384)
Ending balance, fair value of plan assets	106,333	111,934	$ 105,443
Amounts recognized in the consolidated balance sheets consist of:
Pension Non-Current Assets	8,578	8,745
Pension liabilities	0	0
Net amount recognized	8,578	8,745
Amounts recognized in accumulated other comprehensive loss (before income taxes) consist of:
Net actuarial loss	(15,113)	(15,108)
Total loss recognized	$ (15,113)	$ (15,108)
Weighted-average assumptions used to determine pension benefit obligations at year end:
Discount rate	5.20%	4.90%