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
3 Months Ended 12 Months Ended
Sep. 30, 2020
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]        
Value of principal retirement plan $ 14,983      
Contribution plan expense   $ 8,692 $ 8,176 $ 8,685
Class A common stock        
Defined Benefit Plan Disclosure [Line Items]        
Shares contributed to principal retirement plan 668,000      
Pension        
Defined Benefit Plan Disclosure [Line Items]        
Accumulated benefit obligation $ 295,674 295,674 270,140  
Projected benefit obligation $ 318,887 318,887 $ 289,957  
Required plan contribution   $ 4,191    
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) 7.00% 7.00%    
Ultimate health care cost trend rate (as a percent) 4.00% 4.00%    
Effect of one percentage point increase on accumulated postretirement benefit obligation   $ 50    
Effect of one percentage point increase on service and interest cost components   3    
Effect of one percentage point decrease on accumulated postretirement benefit obligation   46    
Effect of one percentage point decrease on service and interest cost components   $ 3