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EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018
Pension |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Service cost | $ 8,223 | $ 7,381 | $ 8,139
Interest cost | 10,587 | 12,173 | 10,493
Expected return on plan assets | (20,579) | (19,054) | (19,639)
Recognized actuarial loss | 10,424 | 5,765 | 7,537
Prior service cost (credit) amortization | 102 | 102 | 106
Net periodic benefit cost | 8,757 | 6,367 | 6,636
Special termination benefit | 0 | 0 | 3,730
Net periodic benefit cost recognized as expense | 8,757 | 6,367 | 10,366
OPEB |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Service cost | 4,854 | 4,404 | 4,607
Interest cost | 7,026 | 8,324 | 6,365
Expected return on plan assets | (6,510) | (5,515) | (5,352)
Recognized actuarial loss | 7,442 | 6,466 | 4,660
Prior service cost (credit) amortization | (197) | (365) | (365)
Net periodic benefit cost | 12,615 | 13,314 | 9,915
Special termination benefit | 0 | 0 | 490
Net periodic benefit cost recognized as expense | $ 12,615 | $ 13,314 | $ 10,405

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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