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Divestitures (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Property, Plant and Equipment Impairment or Disposal [Abstract]    
Proceeds from non-core oil and natural gas asset sales, net of related expenses $ 11.3  
Number of rigs sold 4 1
Net book value of four drilling rigs sold 16.3  
Gain of sale of four drilling rigs $ 9.6