Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Changes In Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details)

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Supplemental Information On Oil And Gas Exploration And Production Activities (Changes In Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Oil and Gas Exploration and Production Industries Disclosures [Abstract]      
Sales and transfers of oil and gas produced, net of production costs $ (194,893) $ (181,723) $ (96,056)
Net changes in prices, production costs, and development costs 108,941 136,071 122,147
Acquisition of oil and gas reserves in place 0 72 63,043
Extensions and discoveries 151,654 107,110 88,227
Revisions of previous quantity estimates, less related production costs (10,504) (112,553) (89,155)
Sales of reserves in place (214,867) 0 0
Accretion of discount 37,668 31,549 24,077
Net changes in income taxes 25,585 (36,674) (54,879)
Change in production rates and other 68,376 117,342 17,309
Total change in standardized measure of discounted future net cash flows $ (28,040) $ 61,194 $ 74,713