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Supplemental Oil and Gas Disclosures (Unaudited) - Changes in Standardized Measure of Discounted Future Net Cash Flow (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]      
Beginning Balance $ 67,498 $ 165,616 $ 136,853
Changes resulting from:      
Net change in sales prices and production costs (3,645) (137,648) 507
Net change in future development costs 0 92 1,308
Sales of oil and gas, net of production costs (5,871) (32,160) (63,979)
Net change due to extensions and discoveries 410 11,747 58,228
Net change due to acquisition of reserves 0 0 2,778
Net change due to divestitures of reserves (63,535) (15,855) (5,804)
Net change due to revisions of quantity estimates 1,367 (15,431) 14,960
Previously estimated development costs incurred 0 (15,096) (15,497)
Accretion of discount 3,105 22,886 18,277
Net change in timing and other (208) 3,808 4,313
Net change in income taxes 11,864 49,347 (17,322)
Aggregate change for the year (56,513) (98,118) 28,763
Ending Balance 10,985 67,498 165,616
Consolidated Entities      
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]      
Beginning Balance 66,796 163,841 135,553
Changes resulting from:      
Net change in sales prices and production costs (3,585) (136,536) (1,064)
Net change in future development costs 0 92 1,308
Sales of oil and gas, net of production costs (5,663) (31,732) (63,192)
Net change due to extensions and discoveries 410 11,747 58,228
Net change due to acquisition of reserves 0 0 2,778
Net change due to divestitures of reserves (63,535) (15,855) (5,804)
Net change due to revisions of quantity estimates 1,304 (15,164) 15,303
Previously estimated development costs incurred 0 (15,096) (15,497)
Accretion of discount 2,992 22,600 18,067
Net change in timing and other (128) 4,018 4,198
Net change in income taxes 11,722 48,689 (17,031)
Aggregate change for the year (56,483) (97,045) 28,288
Ending Balance 10,313 66,796 163,841
Equity Method Investee      
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]      
Beginning Balance 702 1,775 1,300
Changes resulting from:      
Net change in sales prices and production costs (60) (1,112) 1,571
Net change in future development costs 0 0 0
Sales of oil and gas, net of production costs (208) (428) (787)
Net change due to extensions and discoveries 0 0 0
Net change due to acquisition of reserves 0 0 0
Net change due to divestitures of reserves   0 0
Net change due to revisions of quantity estimates 63 (267) (343)
Previously estimated development costs incurred 0 0 0
Accretion of discount 113 286 210
Net change in timing and other (80) (210) 115
Net change in income taxes 142 658 (291)
Aggregate change for the year (30) (1,073) 475
Ending Balance $ 672 $ 702 $ 1,775