Supplemental Oil and Natural Gas Disclosures (Unaudited) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property acquisition costs
Proved
Unproved and unevaluated	28,672	41,497	100,730
Exploration costs	115,084	108,662	60,719
Development costs	190,891	12,511	14,348
Total costs incurred	$ 334,647	$ 162,670	$ 175,797

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

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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- Definition

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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- Definition

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

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- Definition

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

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