Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT PLANS - Weighted Average Asset Allocation and Target Allocation (Details)

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PENSION AND OTHER POSTRETIREMENT PLANS - Weighted Average Asset Allocation and Target Allocation (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Fair value of plan assets $ 158,662 $ 155,634  
Pension      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Fair value of plan assets $ 158,662 155,634 $ 151,864
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Target allocation of plan assets (as a percent) 100.00%    
Equity securities | Pension      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Fair value of plan assets $ 92,745 77,245  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Target allocation of plan assets (as a percent) 50.00%    
Fixed income, cash and cash equivalents | Pension      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Fair value of plan assets $ 44,250 49,008  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Target allocation of plan assets (as a percent) 30.00%    
Other investments | Pension      
Defined Benefit Plan, Actual Plan Asset Allocations [Abstract]      
Fair value of plan assets $ 21,667 $ 29,381  
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Target allocation of plan assets (as a percent) 20.00%