Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Natural Gas Properties (unaudited) (Schedule of Proved Developed and Undeveloped Oil and Gas Reserve Quantities) (Details)

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Supplemental Information on Oil and Natural Gas Properties (unaudited) (Schedule of Proved Developed and Undeveloped Oil and Gas Reserve Quantities) (Details)
 12 Months Ended
Dec. 31, 2015
MBoe
MMcf
MBbls
Dec. 31, 2014
MBoe
MMcf
MBbls
Dec. 31, 2013
MBoe
MMcf
MBbls
Proved developed and undeveloped reserves:      
Beginning of period, MBOE proved developed | MBoe 18,201 7,470 6,735
End of period, MBOE proved developed | MBoe 28,617 18,201 7,470
Beginning of periodc, MBOE proved developed | MBoe 14,623 7,387 7,337
End of period, MBOE proved developed | MBoe 25,654 14,623 7,387
Crude Oil [Member]      
Proved developed and undeveloped reserves:      
Beginning of period | MBbls 25,733 11,898 10,780
Revisions to previous estimates | MBbls (1,632) (243) (2,540)
Purchase of reserves in place | MBbls 2,932 3,223 150
Sale of reserves in place | MBbls (23)   (3,294)
Extensions and discoveries | MBbls 19,127 12,547 7,713
Production | MBbls (2,789) (1,692) (911)
End of period | MBbls 43,348 25,733 11,898
Beginning of period, proved developed | MBbls 14,006 5,960 4,955
End of period, proved developed | MBbls 22,257 14,006 5,960
Beginning of period, proved undeveloped | MBbls 11,727 5,938 5,825
End of period, proved undeveloped | MBbls 21,091 11,727 5,938
Natural Gas [Member]      
Proved developed and undeveloped reserves:      
Beginning of period | MMcf 42,548 17,751 19,753
Revisions to previous estimates | MMcf 4,870 (215) (5,351)
Purchase of reserves in place | MMcf 2,915 8,591 317
Sale of reserves in place | MMcf (105)   (4,576)
Extensions and discoveries | MMcf 19,621 18,641 10,619
Production | MMcf (4,312) (2,220) (3,011)
End of period | MMcf 65,537 42,548 17,751
Beginning of period, proved developed | MMcf 25,171 9,059 10,680
End of period, proved developed | MMcf 38,157 25,171 9,059
Beginning of period, proved undeveloped | MMcf 17,377 8,692 9,073
End of period, proved undeveloped | MMcf 27,380 17,377 8,692