Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT PLANS - Narrative (Details)

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PENSION AND OTHER POSTRETIREMENT PLANS - Narrative (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]      
Contribution plan expense $ 8,176 $ 8,685 $ 8,620
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Accumulated benefit obligation 270,140 224,265  
Projected benefit obligation 289,957 $ 241,553  
Required plan contribution $ 4,333    
Return on plan assets 6.75% 6.75% 6.75%
Other Postretirement      
Defined Benefit Plan Disclosure [Line Items]      
Return on plan assets 0.00% 0.00% 0.00%
Per capita cost of health care benefits assumed for next fiscal year (as a percent) 7.30%    
Ultimate health care cost trend rate (as a percent) 4.00%    
Effect of one percentage point increase on accumulated postretirement benefit obligation $ 718    
Effect of one percentage point increase on service and interest cost components 39    
Effect of one percentage point decrease on accumulated postretirement benefit obligation 629    
Effect of one percentage point decrease on service and interest cost components $ 34