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ASSET RETIREMENT OBLIGATIONS Asset Retirement Obligations (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance beginning of year, January 1 $ 46,566 [1] $ 28,047  
Obligations incurred with development activities and assumed with acquisitions 14,169 9,625  
Accretion of asset retirement obligation 4,060 1,897 1,423
Obligations discharged with disposal of properties and asset retirements (2,232) (990)  
Revisions in estimated cash flows 0 8,903  
Balance end of year, December 31 62,563 46,566 [1] 28,047
Less current portion (1,000) (250)  
Long-term portion 61,563 46,316  
Assets Held for Sale - Asset Retirement Obligations   $ 2,022  
[1] Includes $2 million as of December 31, 2011 related to assets held for sale.