OTHER COMPREHENSIVE INCOME (LOSS) - Summary of OCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ 3,214			$ 8,172			$ 22,387	$ 818
Total other comprehensive income (loss), tax	(475)			530			(1,732)	(109)
Total other comprehensive income (loss), net of taxes	2,739	$ 4,775	$ 13,141	8,702	$ (14,834)	$ 6,841	20,655	709
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,160			9,508			15,022	(493)
Total other comprehensive income (loss), tax	0			0			0	0
Total other comprehensive income (loss), net of taxes	1,160			9,508			15,022	(493)
Pension and other defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,576			1,443			5,311	3,137
Total other comprehensive income (loss), tax	(331)			(304)			(1,115)	(657)
Total other comprehensive income (loss), net of taxes	1,245			1,139			4,196	2,480
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	501			(2,779)			2,077	(1,826)
Total other comprehensive income (loss), tax	(150)			834			(623)	548
Total other comprehensive income (loss), net of taxes	351			(1,945)			1,454	(1,278)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	(23)			0			(23)	0
Total other comprehensive income (loss), tax	6			0			6	0
Total other comprehensive income (loss), net of taxes	$ (17)			$ 0			$ (17)	$ 0