Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Natural Gas Properties (unaudited) (Capitalized Costs Relating to Oil and Natural Gas Activities) (Details)

v3.3.1.900
Supplemental Information on Oil and Natural Gas Properties (unaudited) (Capitalized Costs Relating to Oil and Natural Gas Activities) (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Dec. 31, 2015
USD ($)
$ / Boe
Dec. 31, 2014
USD ($)
$ / Boe
Dec. 31, 2013
USD ($)
$ / Boe
Evaluated Properties          
Beginning of period balance     $ 2,077,985 $ 1,701,577 $ 1,497,010
Capitalized G&A     10,529 10,071 10,014
Property acquisition costs     26,726 94,541 10,885
Exploration costs     81,320 118,251 147,164
Development costs     138,663 153,545 36,504
End of period balance $ 2,335,223   2,335,223 2,077,985 1,701,577
Unevaluated Properties          
Beginning of period balance     142,525 43,222 68,776
Property acquisition costs     5,520 128,342 2,259
Exploration costs     4,576 11,177 10,767
Capitalized interest     10,459 4,295 4,410
Transfers to evaluated     (30,899) (44,511) (42,990)
End of period balance 132,181   132,181 142,525 43,222
Accumulated depreciation, depletion and amortization:          
Beginning of period balance     1,478,355 1,420,612 1,296,265
Provision charged to expense     69,228 56,663 42,251
Write-down of oil and natural gas properties 121,134 $ 87,301 208,435    
Sale of mineral interests       1,080 82,096
End of period balance $ 1,756,018   $ 1,756,018 $ 1,478,355 $ 1,420,612
Depletion expense per physical unit of production | $ / Boe     19.74 27.51 31.12
Lease expense per physical unit of production | $ / Boe     7.71 10.85 14.00
Minimum [Member]          
Accumulated depreciation, depletion and amortization:          
Unevaluated property costs expected evaluation period range     3 years    
Maximum [Member]          
Accumulated depreciation, depletion and amortization:          
Unevaluated property costs expected evaluation period range     5 years