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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - PENSION AND POSTEMPLOYMENT PLANS (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2017 USD ($) plan	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of noncontributory defined benefit retirement plans (in plans) | plan	2
Number of noncontributory medical and life insurance plans (in plans) | plan	2
Pension
Defined Benefit Plan Disclosure [Line Items]
Employer discretionary contributions	$ 0	$ 30,000	$ 0
Employer contributions	74	30,071
OPEB
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 6,049	$ 3,235	$ 5,700

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- Definition

Defined Benefit Plan, Employer Discretionary Contribution Amount

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Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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