OTHER COMPREHENSIVE INCOME (LOSS) - Amounts Reclassified from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total gain (loss)	$ 34,480			$ 20,386			$ 54,360	$ 44,035
Tax benefit (expense)	(12,649)			(6,258)			(21,022)	(14,664)
Net income	21,831	$ 895	$ 10,612	13,595	$ (1,156)	$ 8,753	33,338	21,192
Pension and other defined benefit plans | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total gain (loss)	(1,045)			(226)			(3,137)	(677)
Cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total gain (loss)	556			663			1,550	1,597
Accumulated other comprehensive income (loss), attributable to parent | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total gain (loss)	(489)			437			(1,587)	920
Tax benefit (expense)	102			(92)			333	(193)
Net income	$ (387)			$ 345			$ (1,254)	$ 727