Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (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 (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]      
Future cash flows $ 954,833 $ 1,594,050 $ 1,479,295
Future development and abandonment costs (159,113) (306,810) (301,651)
Future production costs (147,024) (295,383) (305,814)
Future production taxes (89,175) (124,739) (136,323)
Future income taxes (114,867) (229,649) (159,171)
Future net cash flows 444,654 637,469 576,336
10% discount to reflect timing of cash flows (96,013) (260,788) (260,849)
Standardized measure of discounted future net cash flows $ 348,641 $ 376,681 $ 315,487