ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 980,377	$ 980,377	$ 666,692	$ 595,037
Net Change		9,134
Net Change		9,622	(27,777)	590
Ending Balance		$ 1,074,313	$ 980,377	666,692
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201409Member
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustments to AOCI, before tax			$ 0	0
Income tax expense (benefit)			0	0
Effect of the adoption of the stranded tax effect accounting standard		$ (497)
Income tax expense		9
Effect of the adoption of the stranded tax effect accounting standard, net of tax		(488)
Net Change			0	0
Foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustments to AOCI, before tax		19,642	(7,957)	(1,730)
Income tax expense (benefit)		(356)	(591)	2,409
Net Change		19,286	(8,548)	679
Pension and other postretirement, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Adjustments to AOCI, before tax		891	(479)	(25)
Income tax expense (benefit)		156	30	(1)
Net Change		1,047	(449)	(26)
Interest rate swap contract
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Income tax expense (benefit)		3,090	5,411	22
Change in fair value		(23,161)	(23,667)	430
Reclassification adjustment into earnings		9,360	(524)	(515)
Net Change		(10,711)	(18,780)	(63)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ (23,238)	(23,238)	4,539	3,949
Ending Balance		$ (14,104)	$ (23,238)	$ 4,539