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