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Supplementary Information - Standardized Measure of Discounted Future Net Cash Flows and Changes therein Relating to Proved Oil and Gas Reserves (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Sales of oil and gas produced, net of production costs $ (10,426) $ (47,074)
Net changes in prices and production costs (511,116) (18,510)
Extensions, discoveries and improved recovery 24,967 198,235
Revisions of previous quantity estimates (180,048) 67,245
Net change in development costs 235,285 (69,923)
Reserves sold (1,160) (69)
Reserves purchased 737  
Accretion of discount 34,329 23,823
Net change in income taxes 146,339 (56,744)
Changes in production rates (timing) and other (23,393) 8,077
Net change (284,486) 105,060
Standardized measure of discounted future net cash flow:    
Beginning of year 343,288 238,228
End of year $ 58,802 $ 343,288