Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Natural Gas Properties (unaudited) (Oil and Gas Net Production, Average Sales Price and Average Production Costs Disclosure) (Details)

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Supplemental Information on Oil and Natural Gas Properties (unaudited) (Oil and Gas Net Production, Average Sales Price and Average Production Costs Disclosure) (Details)
12 Months Ended
Dec. 31, 2015
$ / Mcfe
$ / Boe
Dec. 31, 2014
$ / Mcfe
$ / Boe
Dec. 31, 2013
$ / Mcfe
$ / Boe
Natural Gas [Member]      
Average Sales Price and Production Costs Per Unit of Production [Line Items]      
Average 12-month price, net of differentials | $ / Mcfe 2.73 6.38 5.45
Crude Oil [Member]      
Average Sales Price and Production Costs Per Unit of Production [Line Items]      
Average 12-month price, net of differentials | $ / Boe 47.25 86.30 92.16