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Summary of Significant Accounting Policies - Additional Information 1 (Detail)
 3 Months Ended
Apr. 27, 2018
USD ($)
Mar. 31, 2018
USD ($)
a
$ / bbl
$ / Mcf
Mar. 31, 2017
USD ($)
Operations And Summary Of Significant Accounting Policies [Line Items]      
Immaterial reduction in prior year debt discount amortization expense included in current period     $ 2,900,000
Loss on sale of oil and gas properties   $ 28,600,000  
Impairment of oil and gas properties   0 0
Cash flow hedges derivative instruments   0  
Commodity Derivatives | Natural Gas Properties      
Operations And Summary Of Significant Accounting Policies [Line Items]      
Gain on derivative financial instruments   $ 2,600,000 $ 7,900,000
South Texas Sold Properties | Subsequent Event      
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    
Post effective date cash flows paid $ 16,000,000    
South Texas Asset Held for Sale      
Operations And Summary Of Significant Accounting Policies [Line Items]      
Undeveloped Acres | a   8,700  
Assets held for sale, fair value   $ 55,000,000  
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%