Postretirement Benefits - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract]
Net gain	$ (854)	$ (191)
Amortization of net loss	30	(7)
Total recognized in other comprehensive income (loss)	(824)	(198)
Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax [Abstract]
Total recognized in net periodic pension cost and other comprehensive income (loss)	$ (198)	$ 593

Defined Benefit Plan, Accumulated Other Comprehensive Income, Amortization of Net Gains (Losses), Before Tax

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- Definition

Amount recognized in net periodic benefit cost (credit) and other comprehensive (income) loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
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- Definition

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
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