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EMPLOYEE BENEFIT PLANS - Fair Value of Pension Plan Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 86,103	$ 91,142	$ 94,897
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	83	161	$ 116
Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	86,103	91,142
Fair Value | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1,541	3,072
Fair Value | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	84,479	67,648
Fair Value | Domestic stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	35,660	17,555
Fair Value | Bond funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,328	18,034
Fair Value | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,447	17,878
Fair Value | International stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14,044	14,181
Fair Value | Domestic common stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		20,261
Fair Value | Oil and gas properties
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	83	161
Fair Value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	86,020	88,468
Fair Value | Level 1 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1,541	3,072
Fair Value | Level 1 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	84,479	67,648
Fair Value | Level 1 | Domestic stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	35,660	17,555
Fair Value | Level 1 | Bond funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,328	18,034
Fair Value | Level 1 | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17,447	17,878
Fair Value | Level 1 | International stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	14,044	14,181
Fair Value | Level 1 | Domestic common stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		17,748
Fair Value | Level 1 | Oil and gas properties
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	2,513
Fair Value | Level 2 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | Domestic stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | Bond funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | International stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 2 | Domestic common stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		2,513
Fair Value | Level 2 | Oil and gas properties
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	83	161
Fair Value | Level 3 | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | Domestic stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | Bond funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | Balanced funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | International stock funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Fair Value | Level 3 | Domestic common stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0
Fair Value | Level 3 | Oil and gas properties
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 83	$ 161

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+ References

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