SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2025	Mar. 31, 2024
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 2,312,684	$ 2,200,443	$ 2,066,201	$ 1,990,735	$ 2,200,443	$ 1,990,735
Amounts reclassified from accumulated other comprehensive loss, net of tax	67		(106)		135	289
Other comprehensive income, before reclassifications, net of tax			9,992			9,992
Net current-period other comprehensive income, net of tax	67	68	9,886	395	135	10,281
Balance as of end of period	2,477,907	2,312,684	2,179,225	2,066,201	2,477,907	2,179,225
Tax on amounts reclassified from accumulated other comprehensive (loss)	(22)		32		(43)	(87)
Tax on other comprehensive income before reclassifications			(3,020)			(3,020)
Tax on net current-period other comprehensive income			(2,988)			(3,107)
Total
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(6,453)	(6,521)	(9,564)	(9,959)	(6,521)	(9,959)
Net current-period other comprehensive income, net of tax	67	68	9,886	395
Balance as of end of period	(6,386)	(6,453)	322	(9,564)	(6,386)	322
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(5,952)	(6,215)	(7,005)	(7,269)	(6,215)	(7,269)
Amounts reclassified from accumulated other comprehensive loss, net of tax	263		262		526	526
Other comprehensive income, before reclassifications, net of tax			0			0
Net current-period other comprehensive income, net of tax			262			526
Balance as of end of period	(5,689)	(5,952)	(6,743)	(7,005)	(5,689)	(6,743)
Tax on amounts reclassified from accumulated other comprehensive (loss)	(80)		(80)		(159)	(159)
Tax on other comprehensive income before reclassifications			0			0
Tax on net current-period other comprehensive income			(80)			(159)
Postemployment Benefit Obligation
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(501)	(306)	(2,559)	(2,690)	(306)	(2,690)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(196)		(368)		(391)	(237)
Other comprehensive income, before reclassifications, net of tax			9,992			9,992
Net current-period other comprehensive income, net of tax			9,624			9,755
Balance as of end of period	(697)	$ (501)	7,065	$ (2,559)	(697)	7,065
Tax on amounts reclassified from accumulated other comprehensive (loss)	$ 58		112		$ 116	72
Tax on other comprehensive income before reclassifications			(3,020)			(3,020)
Tax on net current-period other comprehensive income			$ (2,908)			$ (2,948)