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EMPLOYEE BENEFIT PLANS (Details) (USD $)
1 Months Ended 12 Months Ended
Jan. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Minimum number of years of service for certain employees to be eligible to participate in shared welfare plans that provide postretirement medical and life insurance benefits   5    
Expected long-term return on plan assets   7.75%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets 8.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets 8.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Compensation increase rate - minimum   3.35%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMinimum 3.45%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMinimum 3.20%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMinimum
Compensation increase rate- maximum   3.50%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMaximum 3.50%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMaximum 3.80%ogs_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncreaseMaximum
Description of basis used to determine overall expected long-term rate of return on plan assets   We determine our overall expected long-term rate of return on plan assets, based on our review of historical returns and economic growth models. As of December 31, 2014, we updated our assumed mortality rates to incorporate the new set of mortality tables issued by the Society of Actuaries in October 2014. We determine our discount rates annually.  We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our defined benefit pension and other postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows.  Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds.  Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.    
Increase in regulatory assets as a result of the transfer of unrecognized losses from ONEOK $ 331,000,000ogs_IncreaseinregulatoryassetsasaresultofthetransferofunrecognizedlossesfromONEOK      
Increase in deferred income taxes as a result of the transfer of unrecognized losses from ONEOK 86,000,000ogs_IncreaseindeferredincometaxesasaresultofthetransferofunrecognizedlossesfromONEOK      
Benefit obligation, beginning of period 1,100,000,000us-gaap_DefinedBenefitPlanBenefitObligation 1,100,000,000us-gaap_DefinedBenefitPlanBenefitObligation    
Fair value of plan assets, beginning of period 1,000,000,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets 1,000,000,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets    
Noncurrent liabilities   (287,779,000)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent 0us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent  
Defined Benefit Plan, Amount and Timing of Assets Expected to be Returned to Employer During Following 12 Month Period   0    
Amortization of unrecognized prior service cost   (1,211,000)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit    
Amortization of loss   34,169,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses    
Total recognized in other comprehensive income (loss)   1,781,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax 0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax 0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
Year that the rate reaches the ultimate trend rate   2022    
Defined Benefit Plan, Target Plan Asset Allocations   100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations    
Maximum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Health care cost-trend rate assumed for next year   7.75%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)   5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Minimum [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Health care cost-trend rate assumed for next year   4.00%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)   4.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
ONEOK Profit-Sharing Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expense charged to us by ONEOK, Inc.     1,600,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOKProfitSharingPlanMember
2,100,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOKProfitSharingPlanMember
Expense charged to us by ONEOK, Inc.     1,600,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOKProfitSharingPlanMember
2,100,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOKProfitSharingPlanMember
ONE Gas 401(k) Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Percent of employee contributions matched of eligible compensation (in hundredths)   100.00%ogs_PercentOfEmployeeContributionsMatchedOfEligibleCompensationInHundredths
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEGas401kPlanMember
   
Maximum percentage of each participants eligible compensation subject to certain limits matching (in hundredths)   6.00%ogs_Maximumpercentageofeachparticipantseligiblecompensationsubjecttocertainlimitsmatchinginhundredths
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEGas401kPlanMember
   
Contributions made to 401(k) plan   9,700,000ogs_Contributionsmadeto401kplan
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEGas401kPlanMember
   
ONEOK 401(k) Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Expense charged to us by ONEOK, Inc.     8,300,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOK401kPlanMember
8,400,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOK401kPlanMember
Expense charged to us by ONEOK, Inc.     8,300,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOK401kPlanMember
8,400,000ogs_ExpensechargedtousbyONEOKInc.
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEOK401kPlanMember
ONE Gas Profit-Sharing Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Profit sharing contribution percentage   1.00%ogs_ProfitSharingContributionPercentage
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEGasProfitSharingPlanMember
   
Contributions made to profit-sharing plan   4,000,000ogs_Contributionsmadetoprofitsharingplan
/ ogs_OtherEmployeeBenefitPlansAxis
= ogs_ONEGasProfitSharingPlanMember
   
US Large-Cap Equity [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   37.40%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_USLargeCapEquityMember
   
Investment-grade bonds [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   30.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_InvestmentgradebondsMember
   
Developed foreign large-cap equities [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   10.60%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_DevelopedforeignlargecapequitiesMember
   
Alternative investments [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   7.70%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_AlternativeinvestmentsMember
   
Mid-cap equities [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   5.60%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_MidcapequitiesMember
   
Emerging market equities [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   5.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_EmergingmarketequitiesMember
   
Small-cap equities [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Defined Benefit Plan, Target Plan Asset Allocations   3.70%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= ogs_SmallcapequitiesMember
   
Pension Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic benefit cost   27,071,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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35,000,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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22,800,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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= us-gaap_PensionPlansDefinedBenefitMember
Discount rate   5.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
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= us-gaap_PensionPlansDefinedBenefitMember
4.25%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
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= us-gaap_PensionPlansDefinedBenefitMember
5.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
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= us-gaap_PensionPlansDefinedBenefitMember
Benefit obligation   1,028,171,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_PensionPlansDefinedBenefitMember
   
Fair value of plan assets   845,396,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember
   
Benefit obligation, beginning of period 863,620,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_PensionPlansDefinedBenefitMember
863,620,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_PensionPlansDefinedBenefitMember
   
Service cost   11,620,000us-gaap_DefinedBenefitPlanServiceCost
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Plan participants' contributions   0us-gaap_DefinedBenefitPlanContributionsByPlanParticipants
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Actuarial loss   159,275,000us-gaap_DefinedBenefitPlanActuarialGainLoss
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Benefits paid   (50,135,000)us-gaap_DefinedBenefitPlanBenefitsPaid
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Benefit obligation, end of period   1,028,171,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_PensionPlansDefinedBenefitMember
   
Fair value of plan assets, beginning of period 840,699,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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840,699,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Actual return on plan assets   53,907,000us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
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Employer contributions   925,000us-gaap_DefinedBenefitPlanContributionsByEmployer
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Plan participants' contributions   0us-gaap_DefinedBenefitPlanContributionsByPlanParticipants
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Benefits paid   (50,135,000)us-gaap_DefinedBenefitPlanBenefitsPaid
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Fair value of plan assets, end of period   845,396,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Balance at December 31   (182,775,000)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
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Current liabilities   (907,000)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities
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Noncurrent liabilities   (181,868,000)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
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= us-gaap_PensionPlansDefinedBenefitMember
   
Balance at December 31   (182,775,000)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
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Accumulated benefit obligation for defined benefit pension plans   970,700,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
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Service cost   11,620,000us-gaap_DefinedBenefitPlanServiceCost
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Interest cost   43,791,000us-gaap_DefinedBenefitPlanInterestCost
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Expected return on plan assets   (59,862,000)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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Amortization of unrecognized prior service cost   549,000us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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Amortization of loss   30,200,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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Settlements   773,000us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsAndCurtailments1
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Net periodic benefit cost   27,071,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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35,000,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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22,800,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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Net loss arising during the period   (3,543,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax
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Defined Benefit Plan, Future Amortization of Gain (Loss)   518,000us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss
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Deferred income taxes   1,244,000us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
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Total recognized in other comprehensive income (loss)   (1,781,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
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Prior service credit (cost)   (266,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
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Accumulated loss   (426,862,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
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Accumulated other comprehensive loss before regulatory assets   (427,128,000)ogs_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossBeforeRegulatoryAssetsAndTaxes
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Regulatory asset for regulated entities   418,699,000us-gaap_RegulatoryAssets
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Accumulated other comprehensive loss after regulatory assets   (8,429,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
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Deferred income taxes   3,255,000us-gaap_DeferredTaxLiabilitiesRegulatoryAssets
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Accumulated other comprehensive loss, net of tax   (5,174,000)us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax
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Prior service credit (cost) expected to be recognized in following fiscal year   266,000ogs_Priorservicecreditcostexpectedtoberecognizedinfollowingfiscalyear
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Actuarial net loss, to be recognized in 2015   44,219,000ogs_Actuarialnetlossexpectedtoberecognizedinthefollowingfiscalyear
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Effect of a one percentage point change on total of service and interest cost - increase   484,000us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents
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Effect of a one percentage point change on other postretirement benefit obligation - increase   6,903,000us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation
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Level 3 fair value measurement, January 1 137,044,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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137,044,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Net realized and unrealized gains (losses)   (12,230,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
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Settlements   (7,023,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
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Level 3 fair value measurement, December 31   117,791,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year   900,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
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2015   51,253,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
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2016   52,366,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
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2017   53,622,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
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2018   55,068,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
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2019   56,236,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
2020 through 2024   301,502,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Pension Plan [Member] | Level 1 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   443,317,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Fair value of plan assets, end of period   443,317,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Pension Plan [Member] | Level 2 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   284,288,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Fair value of plan assets, end of period   284,288,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Pension Plan [Member] | Level 3 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   117,791,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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Fair value of plan assets, end of period   117,791,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember
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Other Postretirement Benefit Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Minimum number of years of service for certain employees to be eligible to participate in shared welfare plans that provide postretirement medical and life insurance benefits   5    
Net periodic benefit cost   5,889,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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12,300,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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16,600,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Discount rate   5.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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5.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Benefit obligation   257,688,000us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Fair value of plan assets   151,777,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Benefit obligation, beginning of period 239,171,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
239,171,000us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Service cost   3,468,000us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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Plan participants' contributions   2,642,000us-gaap_DefinedBenefitPlanContributionsByPlanParticipants
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Actuarial loss   14,998,000us-gaap_DefinedBenefitPlanActuarialGainLoss
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Benefits paid   (14,196,000)us-gaap_DefinedBenefitPlanBenefitsPaid
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Benefit obligation, end of period   257,688,000us-gaap_DefinedBenefitPlanBenefitObligation
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Fair value of plan assets, beginning of period 147,237,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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147,237,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Actual return on plan assets   6,912,000us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
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Employer contributions   9,182,000us-gaap_DefinedBenefitPlanContributionsByEmployer
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Plan participants' contributions   2,642,000us-gaap_DefinedBenefitPlanContributionsByPlanParticipants
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Benefits paid   (14,196,000)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Fair value of plan assets, end of period   151,777,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Balance at December 31   (105,911,000)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
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Current liabilities   0us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities
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Noncurrent liabilities   (105,911,000)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
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Balance at December 31   (105,911,000)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
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Service cost   3,468,000us-gaap_DefinedBenefitPlanServiceCost
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Interest cost   11,605,000us-gaap_DefinedBenefitPlanInterestCost
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Expected return on plan assets   (11,393,000)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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Amortization of unrecognized prior service cost   (1,760,000)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
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Amortization of loss   3,969,000us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
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Settlements   0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlementsAndCurtailments1
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Net periodic benefit cost   5,889,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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12,300,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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16,600,000us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
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Net loss arising during the period   0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax
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Defined Benefit Plan, Future Amortization of Gain (Loss)   0us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss
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Deferred income taxes   0us-gaap_IncreaseDecreaseInDeferredIncomeTaxes
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Total recognized in other comprehensive income (loss)   0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
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Prior service credit (cost)   4,337,000us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
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Accumulated loss   (64,861,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax
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Accumulated other comprehensive loss before regulatory assets   (60,524,000)ogs_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossBeforeRegulatoryAssetsAndTaxes
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Regulatory asset for regulated entities   60,524,000us-gaap_RegulatoryAssets
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Accumulated other comprehensive loss after regulatory assets   0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
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Deferred income taxes   0us-gaap_DeferredTaxLiabilitiesRegulatoryAssets
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Accumulated other comprehensive loss, net of tax   0us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax
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Prior service credit (cost) expected to be recognized in following fiscal year   (1,760,000)ogs_Priorservicecreditcostexpectedtoberecognizedinfollowingfiscalyear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Actuarial net loss, to be recognized in 2015   6,040,000ogs_Actuarialnetlossexpectedtoberecognizedinthefollowingfiscalyear
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Effect of a one percentage point change on total of service and interest cost - decrease   (463,000)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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Effect of a one percentage point change on other postretirement benefit obligation - decrease   (6,675,000)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year   3,900,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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2015   13,611,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
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2016   14,283,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2017   15,084,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2018   15,776,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2019   16,398,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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2020 through 2024   88,596,000us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Other Postretirement Benefit Plan [Member] | Level 1 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   50,517,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_FairValueInputsLevel1Member
   
Fair value of plan assets, end of period   50,517,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Other Postretirement Benefit Plan [Member] | Level 2 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   101,165,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   101,165,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Other Postretirement Benefit Plan [Member] | Level 3 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   95,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   95,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Equity Securities [Member] | Pension Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   505,931,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   505,931,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Equity Securities [Member] | Pension Plan [Member] | Level 1 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   439,165,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   439,165,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Equity Securities [Member] | Pension Plan [Member] | Level 2 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   66,766,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   66,766,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Equity Securities [Member] | Pension Plan [Member] | Level 3 [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Equity Securities [Member] | Other Postretirement Benefit Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   62,142,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   62,142,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   251,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Insurance contracts and group annuity contracts [Member] | Pension Plan [Member]        
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Fair value of plan assets, end of period   59,877,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Level 3 fair value measurement, January 1 63,454,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Net realized and unrealized gains (losses)   3,446,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
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Settlements   (7,023,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
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Level 3 fair value measurement, December 31   59,877,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   59,877,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Insurance contracts and group annuity contracts [Member] | Other Postretirement Benefit Plan [Member]        
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Fair value of plan assets, end of period   82,353,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   82,353,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Other Investments [Member] | Pension Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   57,914,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   57,914,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Level 3 fair value measurement, January 1 73,590,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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73,590,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Net realized and unrealized gains (losses)   (15,676,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
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Settlements   0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
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Level 3 fair value measurement, December 31   57,914,000us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Other Investments [Member] | Pension Plan [Member] | Level 3 [Member]        
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Fair value of plan assets   57,914,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   57,914,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Other Investments [Member] | Other Postretirement Benefit Plan [Member]        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Fair value of plan assets   95,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   95,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair value of plan assets, end of period   $ 95,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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