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REGULATORY ASSETS AND LIABILITIES (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Amortization of Regulatory Asset   $ 32,000,000us-gaap_AmortizationOfRegulatoryAsset  
Amortization of Rate Deferral 6,400,000us-gaap_AmortizationOfRateDeferral 21,800,000us-gaap_AmortizationOfRateDeferral 18,300,000us-gaap_AmortizationOfRateDeferral
Regulatory Assets, Current 50,193,000us-gaap_RegulatoryAssetsCurrent 21,657,000us-gaap_RegulatoryAssetsCurrent  
Regulatory Assets, Noncurrent 478,723,000us-gaap_RegulatoryAssetsNoncurrent 23,822,000us-gaap_RegulatoryAssetsNoncurrent  
Regulatory Liability, Current (32,467,000)us-gaap_RegulatoryLiabilityCurrent (17,796,000)us-gaap_RegulatoryLiabilityCurrent  
Net regulatory assets and liabilities, current 17,726,000ogs_Netregulatoryassetsandliabilitiescurrent 3,861,000ogs_Netregulatoryassetsandliabilitiescurrent  
Net regulatory assets and liabilities, noncurrent 463,272,000ogs_Netregulatoryassetsandliabilitiesnoncurrent 2,447,000ogs_Netregulatoryassetsandliabilitiesnoncurrent  
Net Regulatory Assets 480,998,000us-gaap_NetRegulatoryAssets 6,308,000us-gaap_NetRegulatoryAssets  
Accumulated removal costs [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period up to 50 years up to 50 years  
Regulatory Liability, Current 0us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
0us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
 
Regulatory Liability, Noncurrent (15,451,000)us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
(21,375,000)us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
 
Regulatory Liabilities (15,451,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
(21,375,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= us-gaap_AssetRetirementObligationCostsMember
 
Weather normalization [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 1 year    
Regulatory Liability, Current (16,516,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_WeathernormalizationMember
   
Regulatory Liability, Noncurrent 0us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_WeathernormalizationMember
   
Regulatory Liabilities (16,516,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_WeathernormalizationMember
   
Over-recovered purchased-gas costs [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 1 year 1 year  
Regulatory Liability, Current (13,055,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
(17,796,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
 
Regulatory Liability, Noncurrent 0us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
0us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
 
Regulatory Liabilities (13,055,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
(17,796,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_OverrecoveredpurchasedgascostsMember
 
Ad valorem tax [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 1 year    
Regulatory Liability, Current (2,896,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_AdvaloremtaxMember
   
Regulatory Liability, Noncurrent 0us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_AdvaloremtaxMember
   
Regulatory Liabilities (2,896,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_AdvaloremtaxMember
   
Total regulated liabilities [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Liability, Current (32,467,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
(17,796,000)us-gaap_RegulatoryLiabilityCurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
 
Regulatory Liability, Noncurrent (15,451,000)us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
(21,375,000)us-gaap_RegulatoryLiabilityNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
 
Regulatory Liabilities (47,918,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
(39,171,000)us-gaap_RegulatoryLiabilities
/ us-gaap_RegulatoryLiabilityAxis
= ogs_TotalregulatedliabilitiesMember
 
Natural Gas Transition Cost [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Amortization of Regulatory Asset   10,200,000us-gaap_AmortizationOfRegulatoryAsset
/ us-gaap_RegulatoryAssetAxis
= us-gaap_NaturalGasTransitionCostMember
 
Under-recovered purchased-gas costs [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 1 year 1 year  
Regulatory Assets, Current 28,712,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
12,393,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
 
Regulatory Assets, Noncurrent 0us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
0us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
 
Regulatory Assets 28,712,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
12,393,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_UnderrecoveredpurchasedgascostsMember
 
Pension and postretirement benefit costs [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period See Note 12 See Note 12  
Regulatory Assets, Current 18,108,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
298,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
 
Regulatory Assets, Noncurrent 466,684,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
9,556,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
 
Regulatory Assets 484,792,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
9,854,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_PensionCostsMember
 
Reacquired debt costs [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 13 years 14 years  
Regulatory Assets, Current 812,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
812,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
 
Regulatory Assets, Noncurrent 9,730,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
10,541,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
 
Regulatory Assets 10,542,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
11,353,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= us-gaap_LossOnReacquiredDebtMember
 
Other regulatory assets [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Asset, Amortization Period 1 to 24 years 1 to 25 years  
Regulatory Assets, Current 2,561,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
8,154,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
 
Regulatory Assets, Noncurrent 2,309,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
3,725,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
 
Regulatory Assets 4,870,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
11,879,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_OtherregulatoryassetsMember
 
Total regulatory assets, net of amortization [Member]      
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]      
Regulatory Assets, Current 50,193,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember
21,657,000us-gaap_RegulatoryAssetsCurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember
 
Regulatory Assets, Noncurrent 478,723,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember
23,822,000us-gaap_RegulatoryAssetsNoncurrent
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember
 
Regulatory Assets $ 528,916,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember
$ 45,479,000us-gaap_RegulatoryAssets
/ us-gaap_RegulatoryAssetAxis
= ogs_TotalregulatoryassetsnetofamortizationMember