OTHER COMPREHENSIVE INCOME (LOSS) - Summary of OCI (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	$ 8,172			$ (1,055)			$ 818	$ (3,541)
Total other comprehensive income (loss), tax	530			20			(109)	(64)
Total other comprehensive income (loss), net of taxes	8,702	$ (14,834)	$ 6,841	(1,035)	$ 2,880	$ (5,450)	709	(3,605)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	9,508			(1,092)			(493)	(3,943)
Total other comprehensive income (loss), tax	0			0			0	0
Total other comprehensive income (loss), net of taxes	9,508			(1,092)			(493)	(3,943)
Pension and other defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	1,443			236			3,137	708
Total other comprehensive income (loss), tax	(304)			(52)			(657)	(156)
Total other comprehensive income (loss), net of taxes	1,139			184			2,480	552
Cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss), pre-tax	(2,779)			(199)			(1,826)	(306)
Total other comprehensive income (loss), tax	834			72			548	92
Total other comprehensive income (loss), net of taxes	$ (1,945)			$ (127)			$ (1,278)	$ (214)