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SHAREHOLDERS' EQUITY - Schedule of Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands | Jun. 30, 2026 | Sep. 30, 2025
--- | --- | ---
Accumulated Other Comprehensive Income (Loss) |  |
Pre-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | $ 30,123 | $ 49,401
After-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 30,233 | 44,964
Unrealized pension actuarial gain on defined benefit pension plans |  |
Pre-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 4,546 | 3,336
After-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 5,404 | 4,470
Unrealized gain on available-for-sale debt security |  |
Pre-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 0 | 383
After-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 0 | 296
Foreign currency translation adjustment |  |
Pre-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | 25,577 | 45,682
After-tax amounts: |  |
Unrealized pension actuarial gain on defined benefit pension plans | $ 24,829 | $ 40,198

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