Supplemental Oil and Gas Disclosures (Unaudited) - Costs Incurred in Oil and Natural Gas Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves	$ 67,498	$ 165,616	$ 136,853	$ 107,956
Consolidated Entities [Member]
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Cash Inflows	216,588	665,657	544,098
Costs Incurred, Acquisition of Oil and Gas Properties with Proved Reserves	0	2,001	0
Costs Incurred, Acquisition of Unproved Oil and Gas Properties	4,832	25,666	35,806
Exploration costs	17,922	39,399	10,486
Development costs	27,609	40,277	54,538
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities	50,363	107,343	100,830
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Production Costs	93,623	271,735	231,801
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Income Tax Expense	22,218	106,002	77,361
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Net Cash Flows	100,747	287,920	234,936
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Ten Percent Annual Discount for Estimated Timing of Cash Flows	33,951	124,079	99,383
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves	$ 66,796	$ 163,841	$ 135,553	$ 106,543