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Acquisitions and Dispositions - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2017
Jun. 30, 2017
Jun. 30, 2017
Jun. 30, 2016
Business Acquisition [Line Items]        
Purchase of non-controlling interests     $ 61  
Proceeds from sale of property and equipment     46,600  
Capital expenditures, including exploration expense   $ 596 30,463 $ 12,205
Partnership And Trust [Member]        
Business Acquisition [Line Items]        
Purchase of non-controlling interests     $ 60 $ 176
Subsequent Event [Member]        
Business Acquisition [Line Items]        
Proceeds from sale of property and equipment $ 400