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DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details) (USD $) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014 MMcf
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |
Derivative, Nonmonetary Notional Amount |  |  | 16,000 invest_DerivativeNonmonetaryNotionalAmount
Premiums recorded in other current assets on natural gas contracts held |  |  | $ 6,400,000 ogs_Premiumsrecordedinothercurrentassetsonnaturalgascontractsheld
Fair Value Assets, Transfers between Levels | 0 ogs_FairValueAssetsTransfersbetweenLevels | 0 ogs_FairValueAssetsTransfersbetweenLevels |
Long-term Debt, including current maturities | 1,201,310,000 us-gaap_LongTermDebtNoncurrent |  | 1,201,311,000 us-gaap_LongTermDebtNoncurrent
Fair Value, Inputs, Level 1 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |
Fair value, natural gas call options |  |  | 100,000 ogs_Fairvaluenaturalgascalloptions / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Fair Value, Inputs, Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] |  |  |
Long-term Debt, Fair Value | $ 1,300,000,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | $ 1,300,000,000 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member

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- Definition Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
Name: | invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix: | invest_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Definition Amount of transfers of assets measured on a recurring basis between levels of the fair value hierarchy. + References No definition available. + Details
Name: | ogs_FairValueAssetsTransfersbetweenLevels
Namespace Prefix: | ogs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The fair value of purchased natural gas call options held. + References No definition available. + Details
Name: | ogs_Fairvaluenaturalgascalloptions
Namespace Prefix: | ogs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The amount of premiums recorded in other current assets on natural gas contracts held + References No definition available. + Details
Name: | ogs_Premiumsrecordedinothercurrentassetsonnaturalgascontractsheld
Namespace Prefix: | ogs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |