SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE LOSS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 2,000,836	$ 1,784,287	$ 1,817,210	$ 1,630,862
Amounts reclassified from accumulated other comprehensive income, net of tax	304	1,030	913	3,091
Balance as of end of period	1,995,242	1,768,683	1,995,242	1,768,683
Tax on amounts reclassified from accumulated other comprehensive income	(91)	(311)	(275)	(935)
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(7,795)	(8,849)	(8,322)	(9,376)
Amounts reclassified from accumulated other comprehensive income, net of tax	263	262	790	789
Balance as of end of period	(7,532)	(8,587)	(7,532)	(8,587)
Tax on amounts reclassified from accumulated other comprehensive income	(79)	(79)	(238)	(238)
Postemployment Benefit Obligation
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	3,578	(23,618)	3,496	(25,152)
Amounts reclassified from accumulated other comprehensive income, net of tax	41	768	123	2,302
Balance as of end of period	3,619	(22,850)	3,619	(22,850)
Tax on amounts reclassified from accumulated other comprehensive income	(12)	(232)	(37)	(697)
Total
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(4,217)	(32,467)	(4,826)	(34,528)
Balance as of end of period	$ (3,913)	$ (31,437)	$ (3,913)	$ (31,437)