Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation	$ 31,900
Taxes Refundable to Customers	95,739	$ 93,318
Recoverable Future Taxes	181,363	177,261
Federal net operating loss, certain annual limitations	1,800
Deferred Income Taxes [Member]
Income Taxes [Line Items]
Taxes Refundable to Customers	95,700	93,300
Recoverable Future Taxes	181,400	177,300
Regulatory liabilities	52,600	52,600
Regulatory assets	$ 99,400	$ 94,200

Income Taxes [Line Items]

No definition available.

Name:	nfg_IncomeTaxesLineItems
Namespace Prefix:	nfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating Loss Carryforwards, Annual Limitations

+ References

No definition available.

+ Details

Name:	nfg_OperatingLossCarryforwardsAnnualLimitations
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Regulatory assets representing future amounts collectible from customers corresponding to additional deferred income taxes not previously recorded because of ratemaking practices.

+ References

No definition available.

+ Details

Name:	nfg_RecoverableFutureTaxes
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Regulatory assets related to income tax uncertainties, representing future amounts collectible from customers corresponding to additional deferred income taxes not previously recorded because of prior ratemaking practices.

+ References

No definition available.

+ Details

Name:	nfg_RegulatoryAssetsRelatedToIncomeTaxUncertainties
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Noncurrent regulatory liabilities related to income tax uncertainties, representing the reduction of previously recorded deferred income taxes associated with rate-regulated activities that are expected to be refundable to customers as of the end of the period.

+ References

No definition available.

+ Details

Name:	nfg_RegulatoryLiabilitiesRelatedToIncomeTaxUncertainties
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Noncurrent regulatory liability representing the reduction of previously recorded deferred income taxes associated with rate-regulated activities that are expected to be refundable to customers as of the end of the period.

+ References

No definition available.

+ Details

Name:	nfg_TaxesRefundableToCustomers
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

+ Details

Name:	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=nfg_DeferredIncomeTaxesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: