SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2024	Jun. 30, 2023
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 2,179,225	$ 2,066,201	$ 1,990,735	$ 2,000,836	$ 1,922,795	$ 1,817,210	$ 1,990,735	$ 1,817,210
Other comprehensive income, before reclassifications, net of tax							9,992
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(105)			304			184	913
Other comprehensive (loss) income, net of tax	(105)	9,886	395	304	305	304	10,176	913
Balance as of end of period	2,143,018	2,179,225	2,066,201	1,995,242	2,000,836	1,922,795	2,143,018	1,995,242
Tax on other comprehensive income before reclassifications							(3,020)
Tax on amounts reclassified from accumulated other comprehensive income (loss)	33			(91)			(54)	(275)
Tax on net current-period other comprehensive income							(3,074)
Total
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	322	(9,564)	(9,959)	(4,217)	(4,522)	(4,826)	(9,959)	(4,826)
Other comprehensive (loss) income, net of tax	(105)	9,886	395	304	305	304
Balance as of end of period	217	322	(9,564)	(3,913)	(4,217)	(4,522)	217	(3,913)
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(6,743)		(7,269)	(7,795)		(8,322)	(7,269)	(8,322)
Other comprehensive income, before reclassifications, net of tax							0
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	264			263			790	790
Other comprehensive (loss) income, net of tax							790
Balance as of end of period	(6,479)	(6,743)		(7,532)	(7,795)		(6,479)	(7,532)
Tax on other comprehensive income before reclassifications							0
Tax on amounts reclassified from accumulated other comprehensive income (loss)	(79)			(79)			(238)	(238)
Tax on net current-period other comprehensive income							(238)
Postemployment Benefit Obligation
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	7,065		$ (2,690)	3,578		$ 3,496	(2,690)	3,496
Other comprehensive income, before reclassifications, net of tax							9,992
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(369)			41			(606)	123
Other comprehensive (loss) income, net of tax							9,386
Balance as of end of period	6,696	$ 7,065		3,619	$ 3,578		6,696	3,619
Tax on other comprehensive income before reclassifications							(3,020)
Tax on amounts reclassified from accumulated other comprehensive income (loss)	$ 112			$ (12)			184	$ (37)
Tax on net current-period other comprehensive income							$ (2,836)