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Supplemental Oil and Gas Disclosures - Costs Incurred in Oil and Natural Gas Property Acquisition, Exploration and Development Activities (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Acquisition costs:      
Proved oil and gas properties $ 61,874 $ 781,522 $ 28,737
Unproved oil and gas properties 5,424 672 3,226
Exploration costs 11,600 1,792 2,369
Development costs 511,905 207,766 433,735
Asset retirement costs (2,965) 26,795 1,474
Total costs incurred $ 587,838 $ 1,018,547 $ 469,541