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Concentrations (Narrative) (Details)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Customer 1 Concentration Risk
     
Percentage of total oil and natural gas revenues 63.00% 45.00% 51.00%
Customer 2 Concentration Risk
     
Percentage of total oil and natural gas revenues 24.00% 31.00% 17.00%
Customer 3 Concentration Risk
     
Percentage of total oil and natural gas revenues 6.00% 11.00% 12.00%