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Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)
3 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2014
Sep. 30, 2015
Summary Of Significant Accounting Policies [Line Items]        
Gas stored underground - current $ (25,555,000)us-gaap_EnergyRelatedInventoryGasStoredUnderground   $ (39,422,000)us-gaap_EnergyRelatedInventoryGasStoredUnderground  
Capitalized costs of unproved properties excluded from amortization 162,200,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization   141,700,000us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortization  
Full cost ceiling test discount factor 10.00%nfg_FullCostCeilingTestDiscountFactor      
Amount full cost ceiling exceeds book value of oil and gas properties 118,700,000nfg_FullCostCeilingExceedsBookValueOfOilAndGasProperties      
Antidilutive securities 2,461us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 272us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount    
Reserve For Gas Replacement [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Gas stored underground - current 4,028,000us-gaap_EnergyRelatedInventoryGasStoredUnderground
/ us-gaap_StatementBusinessSegmentsAxis
= nfg_ReserveForGasReplacementMember
  0us-gaap_EnergyRelatedInventoryGasStoredUnderground
/ us-gaap_StatementBusinessSegmentsAxis
= nfg_ReserveForGasReplacementMember
 
Stock Options [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Stock options granted 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
     
Restricted Shares [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Share based compensation other than options grants in period 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
     
Stock Appreciation Right [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Share based compensation other than options grants in period 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= nfg_StockAppreciationRightMember
     
Non-performance Based Restricted Stock Units [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Share based compensation other than options grants in period 88,899us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= nfg_NonPerformanceBasedRestrictedStockUnitsMember
     
Granted in fiscal year, weighted average grant date fair value $ 64.04us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= nfg_NonPerformanceBasedRestrictedStockUnitsMember
     
Performance Shares [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Share based compensation other than options grants in period 107,044us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Granted in fiscal year, weighted average grant date fair value $ 65.26us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Subsequent Event [Member] | Reserve For Gas Replacement [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Gas stored underground - current       $ 0us-gaap_EnergyRelatedInventoryGasStoredUnderground
/ us-gaap_StatementBusinessSegmentsAxis
= nfg_ReserveForGasReplacementMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember