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, 2017
Sep. 30, 2016
Sep. 30, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance $ 709,334 $ 734,046 $ 775,206
Net current-period OCI 27,872 (31,631) (83,659)
Ending Balance 790,259 709,334 734,046
Postretirement Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (56,050) (43,474) (39,651)
OCI before reclassification 6,536 (16,901) (7,378)
Amounts reclassified from AOCI 5,891 4,325 3,555
Net current-period OCI 12,427 (12,576) (3,823)
Ending Balance (43,623) (56,050) (43,474)
Currency Translation Adjustment      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (122,259) (104,604) (27,367)
OCI before reclassification 9,352 (17,655) (77,237)
Amounts reclassified from AOCI 0 0 0
Net current-period OCI 9,352 (17,655) (77,237)
Ending Balance (112,907) (122,259) (104,604)
Derivatives      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (3,559) (2,248) 201
OCI before reclassification 7,043 (3,230) (4,841)
Amounts reclassified from AOCI (1,069) 1,919 2,392
Net current-period OCI 5,974 (1,311) (2,449)
Ending Balance 2,415 (3,559) (2,248)
Total      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning Balance (181,868) (150,326) (66,817)
OCI before reclassification 22,931 (37,786) (89,456)
Amounts reclassified from AOCI 4,822 6,244 5,947
Net current-period OCI 27,753 (31,542) (83,509)
Ending Balance (154,115) (181,868) (150,326)
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 277 366 516
OCI before reclassification 119 (89) (150)
Net current-period OCI 119 (89) (150)
Ending Balance 396 277 366
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 277 366 516
OCI before reclassification 119 (89) (150)
Net current-period OCI 119 (89) (150)
Ending Balance $ 396 $ 277 $ 366