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EQUITY (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended 3 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 31, 2015
Jan. 31, 2014
Feb. 17, 2015
Dividends declared per share of stock $ 0.28us-gaap_CommonStockDividendsPerShareCashPaid $ 0.28us-gaap_CommonStockDividendsPerShareCashPaid $ 0.28us-gaap_CommonStockDividendsPerShareCashPaid $ 0.00us-gaap_CommonStockDividendsPerShareCashPaid $ 0.84us-gaap_CommonStockDividendsPerShareCashPaid $ 0.00us-gaap_CommonStockDividendsPerShareCashPaid $ 0.00us-gaap_CommonStockDividendsPerShareCashPaid      
Preferred Stock, Shares Authorized 50us-gaap_PreferredStockSharesAuthorized       50us-gaap_PreferredStockSharesAuthorized       50us-gaap_PreferredStockSharesAuthorized  
Preferred Stock, Par or Stated Value Per Share $ 0.01us-gaap_PreferredStockParOrStatedValuePerShare       $ 0.01us-gaap_PreferredStockParOrStatedValuePerShare          
Common stock authorized and available for issuance 197.9ogs_Commonstockauthorizedandavailableforissuance       197.9ogs_Commonstockauthorizedandavailableforissuance          
Payments of Dividends         $ 43.7us-gaap_DividendsCommonStockCash          
Subsequent Event [Member]                    
Stock Repurchase Program, Authorized Amount                   $ 20us-gaap_StockRepurchaseProgramAuthorizedAmount1
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Dividend Declared [Member]                    
Common Stock, Dividends, Per Share, Declared               $ 0.30us-gaap_CommonStockDividendsPerShareDeclared
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_DividendDeclaredMember
   
Common Stock, Dividends, Declared, Annualized Basis               $ 1.20ogs_CommonStockDividendsDeclaredAnnualizedBasis
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_DividendDeclaredMember