OTHER COMPREHENSIVE INCOME (LOSS) - Summary of OCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ 5,883		$ (14,241)		$ 19,173	$ (7,354)
Total other comprehensive income (loss), tax	(1,108)		(593)		(1,257)	(639)
Total other comprehensive income (loss), net of taxes	4,775	$ 13,141	(14,834)	$ 6,841	17,916	(7,993)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,739		(16,471)		13,862	(10,001)
Total other comprehensive income (loss), tax	0		0		0	0
Total other comprehensive income (loss), net of taxes	1,739		(16,471)		13,862	(10,001)
Pension and other defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,585		847		3,735	1,694
Total other comprehensive income (loss), tax	(340)		(178)		(784)	(353)
Total other comprehensive income (loss), net of taxes	1,245		669		2,951	1,341
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	2,559		1,383		1,576	953
Total other comprehensive income (loss), tax	(768)		(415)		(473)	(286)
Total other comprehensive income (loss), net of taxes	$ 1,791		$ 968		$ 1,103	$ 667