ACCUMULATED OTHER COMPREHENSIVE INCOME - Change in AOCI by Component, Net of Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 868,714	$ 790,259	$ 709,334
OCI before reclassification	(64,578)	(5,374)	22,931
Amounts reclassified from AOCI	515	4,005	4,822
Net current-period OCI	(64,063)	(1,369)	27,753
Reclassification of AOCI tax effects		(8,814)
Ending Balance	719,236	868,714	790,259
Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(37,876)	(43,623)	(56,050)
OCI before reclassification	(36,784)	10,584	6,536
Amounts reclassified from AOCI	2,917	5,047	5,891
Net current-period OCI	(33,867)	15,631	12,427
Reclassification of AOCI tax effects		(9,884)
Ending Balance	(71,743)	(37,876)	(43,623)
Currency Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(134,960)	(112,907)	(122,259)
OCI before reclassification	(21,254)	(22,053)	9,352
Amounts reclassified from AOCI	0	0	0
Net current-period OCI	(21,254)	(22,053)	9,352
Reclassification of AOCI tax effects		0
Ending Balance	(156,214)	(134,960)	(112,907)
Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	8,538	2,415	(3,559)
OCI before reclassification	(6,540)	6,095	7,043
Amounts reclassified from AOCI	(2,402)	(1,042)	(1,069)
Net current-period OCI	(8,942)	5,053	5,974
Reclassification of AOCI tax effects		1,070
Ending Balance	(404)	8,538	2,415
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(164,298)	(154,115)	(181,868)
Reclassification of AOCI tax effects		(8,814)
Ending Balance	(228,361)	(164,298)	(154,115)
Postretirement Benefit Plans attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	0	0	0
OCI before reclassification	0	0	0
Net current-period OCI	0	0	0
Ending Balance	0	0	0
Currency Translation Adjustment attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	467	396	277
OCI before reclassification	(92)	71	119
Net current-period OCI	(92)	71	119
Ending Balance	375	467	396
Derivatives attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	0	0	0
OCI before reclassification	0	0	0
Net current-period OCI	0	0	0
Ending Balance	0	0	0
Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	467	396	277
OCI before reclassification	(92)	71	119
Net current-period OCI	(92)	71	119
Ending Balance	$ 375	$ 467	$ 396

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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