SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2025	Jun. 30, 2024
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 2,477,907	$ 2,312,684	$ 2,200,443	$ 2,179,225	$ 2,066,201	$ 1,990,735	$ 2,200,443	$ 1,990,735
Amounts reclassified from accumulated other comprehensive loss, net of tax	68			(105)			203	184
Other comprehensive income, before reclassifications, net of tax								9,992
Net current-period other comprehensive income, net of tax	68	67	68	(105)	9,886	395	203	10,176
Balance as of end of period	2,423,616	2,477,907	2,312,684	2,143,018	2,179,225	2,066,201	2,423,616	2,143,018
Tax on amounts reclassified from accumulated other comprehensive (loss)	(21)			33			(64)	(54)
Tax on other comprehensive income before reclassifications								(3,020)
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	(6,386)	(6,453)	(6,521)	322	(9,564)	(9,959)	(6,521)	(9,959)
Net current-period other comprehensive income, net of tax	68	67	68	(105)	9,886	395
Balance as of end of period	(6,318)	(6,386)	(6,453)	217	322	(9,564)	(6,318)	217
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(5,689)		(6,215)	(6,743)		(7,269)	(6,215)	(7,269)
Amounts reclassified from accumulated other comprehensive loss, net of tax	264			264			790	790
Other comprehensive income, before reclassifications, net of tax								0
Net current-period other comprehensive income, net of tax								790
Balance as of end of period	(5,425)	(5,689)		(6,479)	(6,743)		(5,425)	(6,479)
Tax on amounts reclassified from accumulated other comprehensive (loss)	(79)			(79)			(238)	(238)
Tax on other comprehensive income before reclassifications								0
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	(697)		$ (306)	7,065		$ (2,690)	(306)	(2,690)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(196)			(369)			(587)	(606)
Other comprehensive income, before reclassifications, net of tax								9,992
Net current-period other comprehensive income, net of tax								9,386
Balance as of end of period	(893)	$ (697)		6,696	$ 7,065		(893)	6,696
Tax on amounts reclassified from accumulated other comprehensive (loss)	$ 58			$ 112			$ 174	184
Tax on other comprehensive income before reclassifications								(3,020)
Tax on net current-period other comprehensive income								$ (2,836)