REGULATORY ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	$ 22,322us-gaap_RegulatoryAssetsCurrent	$ 50,193us-gaap_RegulatoryAssetsCurrent
Regulatory Assets, Noncurrent	465,049us-gaap_RegulatoryAssetsNoncurrent	478,723us-gaap_RegulatoryAssetsNoncurrent
Regulatory Liability, Current	(54,252)us-gaap_RegulatoryLiabilityCurrent	(32,467)us-gaap_RegulatoryLiabilityCurrent
Net regulatory assets (liabilities), current	(31,930)	17,726
Net regulatory assets (liabilities), noncurrent	450,011	463,272
Net Regulatory Assets	418,081us-gaap_NetRegulatoryAssets	480,998us-gaap_NetRegulatoryAssets
Accumulated removal costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	0	0
Regulatory Liability, Noncurrent	(15,038)	(15,451)
Regulatory Liabilities	(15,038)	(15,451)
Weather normalization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	(8,740)	(16,516)
Regulatory Liability, Noncurrent	0	0
Regulatory Liabilities	(8,740)	(16,516)
Over-recovered purchased-gas costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	(44,015)	(13,055)
Regulatory Liability, Noncurrent	0	0
Regulatory Liabilities	(44,015)	(13,055)
Ad valorem tax [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	(1,497)	(2,896)
Regulatory Liability, Noncurrent	0	0
Regulatory Liabilities	(1,497)	(2,896)
Total regulated liabilities [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	(54,252)	(32,467)
Regulatory Liability, Noncurrent	(15,038)	(15,451)
Regulatory Liabilities	(69,290)	(47,918)
Under-recovered purchased-gas costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current		28,712
Regulatory Assets, Noncurrent		0
Regulatory Assets		28,712
Pension and postretirement benefit costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	20,218	18,108
Regulatory Assets, Noncurrent	453,382	466,684
Regulatory Assets	473,600	484,792
Reacquired debt costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	812	812
Regulatory Assets, Noncurrent	9,527	9,730
Regulatory Assets	10,339	10,542
Other regulatory assets [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	1,292	2,561
Regulatory Assets, Noncurrent	2,140	2,309
Regulatory Assets	3,432	4,870
Total regulatory assets, net of amortization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	22,322	50,193
Regulatory Assets, Noncurrent	465,049	478,723
Regulatory Assets	$ 487,371	$ 528,916

The net amount of all current regulatory assets less all current regulatory liabilities as of the end of the period.

No definition available.

Name:	ogs_Netregulatoryassetsandliabilitiescurrent
Namespace Prefix:	ogs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The net amount of noncurrent regulatory assets less all noncurrent regulatory liabilities as of the end of the period.

+ References

No definition available.

+ Details

Name:	ogs_Netregulatoryassetsandliabilitiesnoncurrent
Namespace Prefix:	ogs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	ogs_SCHEDULEOFREGULATEDASSETSANDLIABILITIESLineItems
Namespace Prefix:	ogs_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_NetRegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

+ Details

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

+ Details

Name:	us-gaap_RegulatoryAssetsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

+ Details

Name:	us-gaap_RegulatoryLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

+ Details

Name:	us-gaap_RegulatoryLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ 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 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_RegulatoryLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RegulatoryAssetAxis=ogs_OtherregulatoryassetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=ogs_TotalregulatoryassetsnetofamortizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=ogs_UnderrecoveredpurchasedgascostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=us-gaap_LossOnReacquiredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAssetAxis=us-gaap_PensionCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=ogs_AdvaloremtaxMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=ogs_OverrecoveredpurchasedgascostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=ogs_TotalregulatedliabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=ogs_WeathernormalizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryLiabilityAxis=us-gaap_AssetRetirementObligationCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: