Annual report pursuant to Section 13 and 15(d)

ACCUMULATED OTHER COMPREHENSIVE INCOME - Change in AOCI by Component, Net of Tax (Details)

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ACCUMULATED OTHER COMPREHENSIVE INCOME - Change in AOCI by Component, Net of Tax (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance $ 790,259 $ 709,334 $ 734,046
Net current-period OCI (1,298) 27,872 (31,631)
Ending Balance 868,714 790,259 709,334
Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (43,623) (56,050) (43,474)
OCI before reclassification 10,584 6,536 (16,901)
Amounts reclassified from AOCI 5,047 5,891 4,325
Reclassification of AOCI tax effects (9,884)    
Net current-period OCI 15,631 12,427 (12,576)
Ending Balance (37,876) (43,623) (56,050)
Currency Translation Adjustment      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (112,907) (122,259) (104,604)
OCI before reclassification (22,053) 9,352 (17,655)
Amounts reclassified from AOCI 0 0 0
Reclassification of AOCI tax effects 0    
Net current-period OCI (22,053) 9,352 (17,655)
Ending Balance (134,960) (112,907) (122,259)
Derivatives      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance 2,415 (3,559) (2,248)
OCI before reclassification 6,095 7,043 (3,230)
Amounts reclassified from AOCI (1,042) (1,069) 1,919
Reclassification of AOCI tax effects 1,070    
Net current-period OCI 5,053 5,974 (1,311)
Ending Balance 8,538 2,415 (3,559)
Total      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (154,115) (181,868) (150,326)
OCI before reclassification (5,374) 22,931 (37,786)
Amounts reclassified from AOCI 4,005 4,822 6,244
Reclassification of AOCI tax effects (8,814)    
Net current-period OCI (1,369) 27,753 (31,542)
Ending Balance (164,298) (154,115) (181,868)
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 396 277 366
OCI before reclassification 71 119 (89)
Net current-period OCI 71 119 (89)
Ending Balance 467 396 277
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 277 277 366
OCI before reclassification 71 119 (89)
Net current-period OCI 71 119 (89)
Ending Balance $ 348 $ 277 $ 277