Supplemental Oil and Gas Disclosures (Unaudited) - Costs Incurred in Oil and Natural Gas Property Acquisition, Exploration and Development (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
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	$ 165,616	$ 136,853	$ 107,956	$ 56,206
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Entity's Share of Equity Method Investees' Standardized Discounted Future Net Cash Flows	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	665,657	544,098	322,098
Costs Incurred, Acquisition of Oil and Gas Properties with Proved Reserves	2,001	0	0
Costs Incurred, Acquisition of Unproved Oil and Gas Properties	25,666	35,806	4,418
Exploration costs	39,399	10,486	1,752
Development costs	40,277	54,538	15,938
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities	107,343	100,830	22,108
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Production Costs	271,735	231,801	104,441
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Income Tax Expense	106,002	77,361	50,350
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Net Cash Flows	287,920	234,936	167,307
Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Ten Percent Annual Discount for Estimated Timing of Cash Flows	124,079	99,383	60,764
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves	$ 163,841	$ 135,553	$ 106,543	$ 52,698

Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have proved reserves.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

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Costs incurred, including capitalized costs and costs charged to expense, associated with the acquisition of oil and gas properties that have unproved reserves.

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Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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Exploration costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

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-Publisher FASB

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Amount of costs incurred related to oil and gas property acquisition, exploration and development activities, including capitalized costs and costs charged to expense.

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The enterprise's share of the investees' standardized measure of discounted future net cash flows for the period, in the aggregate and by each geographic area for which quantities are disclosed. This information is excluded from the enterprise's standardized measure and is disclosed separately if the financial statements of the reporting enterprise include investments that are accounted for by the equity method.

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Amount of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and gas reserves.

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Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

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Amount of estimated future accumulated cash outflow for costs to be incurred in producing proved oil and gas reserves.

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Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year.

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Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves.

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