OTHER COMPREHENSIVE INCOME (LOSS) - AOCI (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Class of Stock [Line Items]
Accumulated other comprehensive income (loss)	$ 476,454	$ 494,693	$ 477,763	$ 474,284	$ 471,561	$ 474,391
Foreign currency translation adjustments
Class of Stock [Line Items]
Accumulated other comprehensive income (loss)	(41,285)		(31,284)
Pension and other defined benefit plans
Class of Stock [Line Items]
Accumulated other comprehensive income (loss)	(33,473)		(34,814)
Cash flow hedges
Class of Stock [Line Items]
Accumulated other comprehensive income (loss)	849		182
Accumulated other comprehensive income (loss), attributable to parent
Class of Stock [Line Items]
Accumulated other comprehensive income (loss)	$ (73,909)	$ (59,075)	$ (65,916)	$ (36,682)	$ (39,562)	$ (34,112)