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Summary Of Significant Accounting Policies (Components Of Other Current Assets) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Sep. 30, 2014
Summary Of Significant Accounting Policies [Line Items]    
Prepayments $ 5,314us-gaap_OtherPrepaidExpenseCurrent $ 10,079us-gaap_OtherPrepaidExpenseCurrent
Prepaid Property and Other Taxes 22,266us-gaap_PrepaidTaxes 13,743us-gaap_PrepaidTaxes
Fair Values of Firm Commitments 14,694nfg_OtherCurrentAssetsFairValuesOfFirmCommitments 0nfg_OtherCurrentAssetsFairValuesOfFirmCommitments
Regulatory Assets 17,318us-gaap_RegulatoryAssetsCurrent 22,719us-gaap_RegulatoryAssetsCurrent
Other Current Assets 59,592us-gaap_OtherAssetsCurrent 54,752us-gaap_OtherAssetsCurrent
Federal [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Income Taxes Receivable $ 0us-gaap_IncomeTaxReceivable
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember
$ 8,211us-gaap_IncomeTaxReceivable
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember