Retirement Plan And Other Post-Retirement Benefits (Schedule Of Significant Unobservable Input Changes In Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, Beginning of Year	$ 436	$ 2,931
Unrealized Gains/(Losses)	(141)	(2,495)
Sales	0	0
Balance, End of Year	295	436
Retirement Plan [Member] \| Excluding 401(h) Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, Beginning of Year	(35)	(223)
Unrealized Gains/(Losses)	11	188
Sales	0	0
Balance, End of Year	(24)	(35)
Retirement Plan [Member] \| Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, Beginning of Year	471	3,154
Unrealized Gains/(Losses)	(152)	(2,683)
Sales	0	0
Balance, End of Year	319	471
Other Post-Retirement Benefit Plans [Member] \| 401(h) Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Balance, Beginning of Year	35	223
Unrealized Gains/(Losses)	(11)	(188)
Sales	0	0
Balance, End of Year	$ 24	$ 35

This element represents total unrealized gains or losses for the period arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

No definition available.

+ Details

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Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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Period Type:	instant

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- Details

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