Seismic and Exploration Expenses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	89 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013
Seismic and Exploration Expenses
Seismic costs	$ 18,109	$ 15,214	$ 360,157
Seismic cost recovery			(25,126)
Leasehold delay rentals	1,387	1,409	34,289
Force Majeure expense			13,549
Drilling rig expense	2,822	727	29,621
Total seismic and exploration expenses	$ 22,318	$ 17,350	$ 412,490

The costs incurred to retain exploration and property rights after acquisition but before production has occurred. Costs include legal costs for title defense, ad valorem taxes on nonproducing mineral properties, shut-in royalties, and delay rentals.

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Exploration expenses (including prospecting) related to oil and gas producing entities and would be included in operating expenses of that entity. Costs incurred in identifying areas that may warrant examination and in examining specific areas that are considered to have prospects of containing oil and gas reserves, including costs of drilling exploratory wells and exploratory-type stratigraphic test wells. Exploration costs may be incurred both before acquiring the related property (sometimes referred to in part as prospecting costs) and after acquiring the property. Principal types of exploration costs, which include depreciation and applicable operating costs of support equipment and facilities and other costs of exploration activities, are: (i) Costs of topographical, geographical and geophysical studies, rights of access to properties to conduct those studies, and salaries and other expenses of geologists, geophysical crews, and others conducting those studies. Collectively, these are sometimes referred to as geological and geophysical or "G&G" costs. (ii) Costs of carrying and retaining undeveloped properties, such as delay rentals, ad valorem taxes on properties, legal costs for title defense, and the maintenance of land and lease records. (iii) Dry hole contributions and bottom hole contributions. (iv) Costs of drilling and equipping exploratory wells. (v) Costs of drilling exploratory-type stratigraphic test wells.

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- Definition

Costs incurred to operate and maintain an entities' wells and related equipment and facilities, including depreciation and applicable operating costs of support equipment and facilities and other costs of operating and maintaining those wells and related equipment and facilities.

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