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)

v3.8.0.1
Supplemental Information on Oil and Natural Gas Properties (unaudited) (Capitalized Costs Relating to Oil and Natural Gas Activities) (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Evaluated Properties          
Beginning of period balance   $ 2,335,223 $ 2,754,353 $ 2,335,223 $ 2,077,985
Capitalized G&A expenses     11,982 12,222 10,529
Property acquisition costs     144,358 216,561 26,726
Exploration costs     239,453 38,612 81,320
Development costs     279,424 151,735 138,663
End of period balance     3,429,570 2,754,353 2,335,223
Unevaluated Properties          
Beginning of period balance   132,181 668,721 132,181 142,525
Property acquisition costs     590,308 548,673 5,520
Exploration costs     6,374 8,631 4,576
Capitalized interest expenses     33,783 19,857 10,459
Transfers to Evaluated Properties     (131,170) (40,621) (30,899)
End of period balance     1,168,016 668,721 132,181
Accumulated depreciation, depletion and amortization:          
Beginning of period balance   1,756,018 1,947,673 1,756,018 1,478,355
Provision charged to expense     115,897 71,330 69,228
Write-down of oil and natural gas properties $ 61,012 $ 34,776 0 95,788 208,435
Sale of mineral interests and equipment     20,525 24,537 0
End of period balance     $ 2,084,095 $ 1,947,673 $ 1,756,018