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Oil and natural gas properties (Tables)
 12 Months Ended
Dec. 31, 2015
Extractive Industries [Abstract]  
Schedule of oil and natural gas properties
Oil and natural gas properties are comprised of the following:
 
 
 December 31,
 
2015
 
2014
Proved property
$
9,940,660

 
$
8,903,060

Unproved property
1,375,940

 
1,365,951

Work in process
—

 
—

Total oil and natural gas properties, at cost
11,316,600

 
10,269,011

Less: accumulated impairment
(8,283,321
)
 
(7,430,438
)
Oil and natural gas properties, net of impairment
3,033,279

 
2,838,573

Less: accumulated depletion
(2,274,188
)
 
(1,942,380
)
Oil and natural gas properties, net
$
759,091

 
$
896,193