Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT PLANS - Fair Value Allocation of Plan Assets (Details)

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PENSION AND OTHER POSTRETIREMENT PLANS - Fair Value Allocation of Plan Assets (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets $ 208,344 $ 168,134
Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 92,900 132,775
Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 101,133 20,086
Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 14,311 15,273
Equity securities - stocks    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 4,075 37,089
Equity securities - stocks | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 4,075 37,089
Equity securities - stocks | Level 1 | Class A common stock    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 4,075 14,936
Equity securities - stocks | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Equity securities - stocks | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Equity securities - mutual funds    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets   81,588
Equity securities - mutual funds | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets   81,588
Equity securities - mutual funds | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets   0
Equity securities - mutual funds | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets   0
Fixed income securities    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 111,536 31,824
Fixed income securities | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 10,403 11,738
Fixed income securities | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 101,133 20,086
Fixed income securities | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Cash and cash equivalents    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 78,422 2,360
Cash and cash equivalents | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 78,422 2,360
Cash and cash equivalents | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Cash and cash equivalents | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Other investments    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 14,311 15,273
Other investments | Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Other investments | Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets 0 0
Other investments | Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets $ 14,311 $ 15,273