OTHER COMPREHENSIVE INCOME (LOSS) - Summary of OCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ (14,241)		$ 2,822		$ (7,354)	$ (2,486)
Total other comprehensive income (loss), tax	(593)		58		(639)	(84)
Total other comprehensive income (loss), net of taxes	(14,834)	$ 6,841	2,880	$ (5,450)	(7,993)	(2,570)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	(16,471)		2,885		(10,001)	(2,851)
Total other comprehensive income (loss), tax	0		0		0	0
Total other comprehensive income (loss), net of taxes	(16,471)		2,885		(10,001)	(2,851)
Pension and other defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	847		201		1,694	472
Total other comprehensive income (loss), tax	(178)		(17)		(353)	(104)
Total other comprehensive income (loss), net of taxes	669		184		1,341	368
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,383		(264)		953	(107)
Total other comprehensive income (loss), tax	(415)		75		(286)	20
Total other comprehensive income (loss), net of taxes	$ 968		$ (189)		$ 667	$ (87)