SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2024	Mar. 31, 2023
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	$ 2,066,201	$ 1,990,735	$ 1,922,795	$ 1,817,210	$ 1,990,735	$ 1,817,210
Other comprehensive (loss) income, before reclassifications, net of tax	9,992				9,992
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(106)		305		289	609
Other comprehensive income, net of tax	9,886	395	305	304	10,281	609
Balance as of end of period	2,179,225	2,066,201	2,000,836	1,922,795	2,179,225	2,000,836
Tax on other comprehensive income before reclassifications	(3,020)				(3,020)
Tax on amounts reclassified from accumulated other comprehensive income (loss)	32		(93)		(87)	(184)
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	(9,564)	(9,959)	(4,522)	(4,826)	(9,959)	(4,826)
Other comprehensive income, net of tax	9,886	395	305	304
Balance as of end of period	322	(9,564)	(4,217)	(4,522)	322	(4,217)
Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Balance as of beginning of period	(7,005)	(7,269)	(8,059)	(8,322)	(7,269)	(8,322)
Other comprehensive (loss) income, before reclassifications, net of tax	0				0
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	262		264		526	527
Other comprehensive income, net of tax	262				526
Balance as of end of period	(6,743)	(7,005)	(7,795)	(8,059)	(6,743)	(7,795)
Tax on other comprehensive income before reclassifications	0				0
Tax on amounts reclassified from accumulated other comprehensive income (loss)	(80)		(80)		(159)	(159)
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	(2,559)	(2,690)	3,537	3,496	(2,690)	3,496
Other comprehensive (loss) income, before reclassifications, net of tax	9,992				9,992
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(368)		41		(237)	82
Other comprehensive income, net of tax	9,624				9,755
Balance as of end of period	7,065	$ (2,559)	3,578	$ 3,537	7,065	3,578
Tax on other comprehensive income before reclassifications	(3,020)				(3,020)
Tax on amounts reclassified from accumulated other comprehensive income (loss)	112		$ (13)		72	$ (25)
Tax on net current-period other comprehensive income	$ (2,908)				$ (2,948)