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 ($)
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]      
Contribution plan expense $ 8,685,000 $ 8,620,000 $ 8,117,000
Change in Assumptions for Pension Plans      
Defined Benefit Plan Disclosure [Line Items]      
Reduction in service and interest cost 1,960,000    
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Accumulated benefit obligation 224,265,000 238,307,000  
Projected benefit obligation 241,553,000 $ 259,672,000  
Required plan contribution $ 0    
Target allocation of plan assets (as a percent) 100.00%    
Return on plan assets 6.75% 6.75% 7.25%
Pension | Equity securities      
Defined Benefit Plan Disclosure [Line Items]      
Target allocation of plan assets (as a percent) 50.00%    
Pension | Fixed income, cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Target allocation of plan assets (as a percent) 30.00%    
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) 7.80%    
Ultimate health care cost trend rate (as a percent) 4.00%    
Effect of one percentage point increase on accumulated postretirement benefit obligation $ 705,000    
Effect of one percentage point increase on service and interest cost components 46,000    
Effect of one percentage point decrease on accumulated postretirement benefit obligation 622,000    
Effect of one percentage point decrease on service and interest cost components $ 40,000