POSTRETIREMENT BENEFITS - Asset Allocations by Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 106,333	$ 111,934	$ 105,443
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	102,744	107,471
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,589	4,463
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,978	38,540
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,389	34,077
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,589	4,463
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71,355	73,394
Level 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71,355	73,394
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0