Annual report pursuant to Section 13 and 15(d)

ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of AOCI (Details)

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ACCUMULATED OTHER COMPREHENSIVE INCOME - Reclassifications out of AOCI (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Derivatives      
Interest expense $ (26,371) $ (24,344) $ (20,610)
Income before income tax 96,287 95,234 89,652
Income taxes (22,354) (29,073) (26,364)
Net income 73,933 66,161 63,288
Prior service (cost) credit      
Postretirement benefit plans      
Income before income tax 376 378 375
Actuarial losses      
Postretirement benefit plans      
Income before income tax (10,034) (7,468) (6,203)
Postretirement Benefit Plans      
Postretirement benefit plans      
Income before income tax (9,658) (7,090) (5,828)
Income taxes (3,767) (2,765) (2,273)
Net income (5,891) (4,325) (3,555)
Derivatives      
Postretirement benefit plans      
Net income 1,069 (1,919) (2,392)
Derivatives | Reclassification out of Accumulated Other Comprehensive Income      
Derivatives      
Interest expense 1,752 (3,146) (3,922)
Income before income tax 1,752 (3,146) (3,922)
Income taxes (683) 1,227 1,530
Net income $ 1,069 $ (1,919) $ (2,392)