Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Natural Gas Reserve Data (unaudited) (Summarized Average 12-month Oil and Natural Gas Prices Net of Differentials) (Details)

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Supplemental Oil and Natural Gas Reserve Data (unaudited) (Summarized Average 12-month Oil and Natural Gas Prices Net of Differentials) (Details)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Natural Gas [Member]
     
Average Sales Price and Production Costs Per Unit of Production [Line Items]      
Average 12-month price, net of differentials 5.45 4.81 5.60
Crude Oil [Member]
     
Average Sales Price and Production Costs Per Unit of Production [Line Items]      
Average 12-month price, net of differentials 92.16 94.68 98.98