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Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Acquisitions:    
Acreage purchases [1] $ 41,817 $ 33,142
Oil and gas properties [1] 7,875 3,098,772
Asset retirement obligations [1]   21,908
Development [1] 809,961 497,795
Exploration:    
Exploration drilling costs incurred [1] 1,008 37,680
Gas gathering facilities:    
Development [1] 6,292 3,595
Subtotal [1] 912,722 3,725,217
Asset retirement obligations [1] 6,460 (24,064)
Total costs incurred [1] 919,182 3,701,153
Expense    
Exploration:    
Exploration costs incurred [1] 44,173 30,027
Stock-based compensation expense [1] $ 1,596 $ 2,298
[1] Includes costs incurred whether capitalized or expensed.