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EMPLOYEE BENEFIT PLANS - COMPONENTS OF NET PERIODIC COST (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Pension |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Service cost | $ 8,139 | [1] | $ 8,347 | [1] | $ 7,591
Interest cost | 10,493 | [1] | 9,771 | [1] | 11,342
Expected return on plan assets | (19,639) |  | (19,313) |  | (20,118)
Recognized actuarial loss | 7,537 |  | 8,827 |  | 7,281
Prior service cost (credit) amortization | 106 |  | 111 |  | 111
Net periodic benefit cost | 6,636 |  | 7,743 |  | 6,207
Special termination benefit | 3,730 | [1],[2] | 0 | [1],[2] | 0
Net periodic benefit cost recognized as expense | 10,366 |  | 7,743 |  | 6,207
OPEB |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Service cost | 4,607 |  | 4,380 |  | 4,521
Interest cost | 6,365 |  | 5,545 |  | 6,256
Expected return on plan assets | (5,352) |  | (4,767) |  | (4,845)
Recognized actuarial loss | 4,660 |  | 4,370 |  | 3,274
Prior service cost (credit) amortization | (365) |  | (365) |  | (365)
Net periodic benefit cost | 9,915 |  | 9,163 |  | 8,841
Special termination benefit | 490 | [2] | 0 | [2] | 0
Net periodic benefit cost recognized as expense | $ 10,405 |  | $ 9,163 |  | $ 8,841
[1] | Includes the Company’s PEP.
[2] | Related to the voluntary early retirement program offered during fiscal 2018, as previously discussed.

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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 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: 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=112275985&loc=d3e4179-114921 Reference 3: 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=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) 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=112275985&loc=d3e4179-114921 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)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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