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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 4) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Fixed assets      
Accrued asset retirement obligations $ 2.7us-gaap_AssetRetirementObligation $ 2.2us-gaap_AssetRetirementObligation  
Impairment of fixed assets $ 0us-gaap_TangibleAssetImpairmentCharges $ 0us-gaap_TangibleAssetImpairmentCharges $ 0us-gaap_TangibleAssetImpairmentCharges
Minimum      
Fixed assets      
Useful life 3 years    
Maximum      
Fixed assets      
Useful life 39 years