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EMPLOYEE BENEFIT PLANS - SUMMARY OF CHANGE IN FUNDED STATUS AND LIABILITIES (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2024 | Jan. 02, 2024 | Mar. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Sep. 30, 2023
Postemployment employee (liability) |  |  |  |  |  |
Noncurrent | $ (42,333) |  |  | $ (42,333) |  | $ (102,528)
OPEB |  |  |  |  |  |
Change in Benefit Obligation |  |  |  |  |  |
Benefit obligation at beginning of period |  | $ 203,406 |  | 203,406 | $ 173,217 | 173,217
Service cost | 255 | 642 | $ 618 | 897 | 1,236 | 2,471
Interest cost | $ 1,808 | 2,902 | $ 2,287 | 4,710 | 4,573 | 9,146
Plan amendments |  | (81,283) |  |  |  | 0
Plan participants’ contributions |  | 0 |  |  |  | 552
Actuarial loss |  | 26,871 |  |  |  | 25,363
Benefits paid, net of retiree subsidies received |  | (1,614) |  |  |  | (7,343)
Benefit obligation at end of period |  | 150,924 |  |  |  | 203,406
Change in plan assets |  |  |  |  |  |
Fair value of plan assets at beginning of period |  | 106,783 |  | $ 106,783 | $ 99,736 | 99,736
Actual return on plan assets |  | 8,995 |  |  |  | 9,826
Employer contributions |  | 3,181 |  |  |  | 4,192
Benefits paid, net of plan participants’ contributions |  | (1,612) |  |  |  | (6,971)
Fair value of plan assets at end of period |  | 117,347 |  |  |  | 106,783
Funded status |  | (33,577) |  |  |  | (96,623)
Postemployment employee (liability) |  |  |  |  |  |
Current |  | (1,613) |  |  |  | (4,201)
Noncurrent |  | (31,964) |  |  |  | (92,422)
Total |  | $ (33,577) |  |  |  | $ (96,623)

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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