Oil and Natural Gas Activities--Costs Incurred (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property acquisition costs
Proved properties	$ 3,496	$ 69,962	$ 1,108
Unproved properties	84,938	145,853	46,895
Total acquisition costs	88,434	215,815	48,003
Development costs	561,578us-gaap_CostsIncurredDevelopmentCosts	376,394us-gaap_CostsIncurredDevelopmentCosts	409,429us-gaap_CostsIncurredDevelopmentCosts
Exploration costs	90,146us-gaap_CostsIncurredExplorationCosts	77,507us-gaap_CostsIncurredExplorationCosts	54,432us-gaap_CostsIncurredExplorationCosts
Total	$ 740,158	$ 669,716	$ 511,864

Cost incurred, including capitalized costs and costs charged to expense, in acquisition of oil and gas properties.

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-Name Accounting Standards Codification

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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 proved reserves.

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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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-Glossary Exploration

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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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