SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE LOSS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 1,922,795	$ 1,716,978	$ 1,817,210	$ 1,630,862
Amounts reclassified from accumulated other comprehensive income, net of tax	305	1,031	609	2,061
Balance as of end of period	2,000,836	1,784,287	2,000,836	1,784,287
Tax on amounts reclassified from accumulated other comprehensive income	(93)	(312)	(184)	(624)
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(8,059)	(9,112)	(8,322)	(9,376)
Amounts reclassified from accumulated other comprehensive income, net of tax	264	263	527	527
Balance as of end of period	(7,795)	(8,849)	(7,795)	(8,849)
Tax on amounts reclassified from accumulated other comprehensive income	(80)	(80)	(159)	(159)
Postemployment Benefit Obligation
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	3,537	(24,386)	3,496	(25,152)
Amounts reclassified from accumulated other comprehensive income, net of tax	41	768	82	1,534
Balance as of end of period	3,578	(23,618)	3,578	(23,618)
Tax on amounts reclassified from accumulated other comprehensive income	(13)	(232)	(25)	(465)
Total
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(4,522)	(33,498)	(4,826)	(34,528)
Balance as of end of period	$ (4,217)	$ (32,467)	$ (4,217)	$ (32,467)