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Summary of Significant Accounting Policies - Additional Information 1 (Detail)
3 Months Ended 6 Months Ended
Apr. 27, 2018
USD ($)
Jun. 30, 2018
USD ($)
a
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
a
$ / bbl
$ / Mcf
Jun. 30, 2017
USD ($)
Operations And Summary Of Significant Accounting Policies [Line Items]          
Loss on sale of oil and gas properties   $ 6,838,000   $ 35,438,000  
Loss resulting from final settlement for property sale   2,700,000   2,700,000  
Impairment of oil and gas properties   0 $ 0 0 $ 0
Cash flow hedges derivative instruments   $ 0   $ 0  
South Texas Sold Properties          
Operations And Summary Of Significant Accounting Policies [Line Items]          
Gross proceeds from sale of oil and gas properties $ 125,000,000        
Effective date of sale Nov. 01, 2017        
South Texas Asset Held for Sale          
Operations And Summary Of Significant Accounting Policies [Line Items]          
Undeveloped Acres | a   8,400   8,400  
Assets held for sale, fair value   $ 55,000,000   $ 55,000,000  
Loss on sale of oil and gas properties   $ 4,100,000   $ 32,700,000  
Management's oil price outlook | $ / bbl       72.03  
Management's gas price outlook | $ / Mcf       4.31  
Annual minimum discount rate       20.00%  
Annual maximum discount rate       25.00%