Basis of Presentation Basis of Presentation (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Mar. 31, 2013
Assets
Oil and gas properties - proved		$ 247,709
Oil and gas properties - unproved		172,367
Other assets		15,100
Total assets		435,176
Liabilities
Accounts payable and accrued expenses		(31,000)
Other liabilities		(1,500)
Total liabilities		(32,500)
Net asset acquired		402,676
Business Acquisition, Pro Forma Information [Abstract]
Total revenues	389,260
Net loss	$ (160,555)
Loss per share - basic and diluted	$ (2.77)

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Business Acquisition, Purchase Price Allocation, Proved Properties

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The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The amount of acquisition cost of a business combination allocated to assets acquired.

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The total purchase price of the acquired entity. This includes cash paid to equity interest holders of the acquired entity, fair value of debt and equity securities issued to equity holders of the acquired entity, and transaction costs paid to third parties to consummate the acquisition.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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