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Leases - Balance Sheet Information Related to Operating Leases (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Assets: |  |
Deferred Charges | $ 41,317 | $ 44,206
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] | Deferred Charges | Deferred Charges
Liabilities: |  |
Other Accruals and Current Liabilities | $ 11,479 | $ 11,518
Other Liabilities | $ 29,683 | $ 32,616
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] | Other Accruals and Current Liabilities | Other Accruals and Current Liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] | Other Liabilities | Other Liabilities

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- Definition Operating Lease, Asset + References No definition available. + Details
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Namespace Prefix: | nfg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-1 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | instant

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- Definition Indicates line item in statement of financial position that includes current operating lease liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-2 + Details
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-1 + Details
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Balance Type: | credit
Period Type: | instant

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- Definition Indicates line item in statement of financial position that includes noncurrent operating lease liability. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-2 + Details
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- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-1 + Details
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Balance Type: | debit
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- Definition Indicates line item in statement of financial position that includes operating lease right-of-use asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-2 + Details
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