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Supplemental Financial Information Exploration and Production (Details 3) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items] |  |  |  |  |  |
Results of Operations, Sales or Transfers to Entity's Other Operations | $ 93,713 |  | $ 115,784 |  | $ 101,230 |
Results of Operations, Sales Revenue to Unaffiliated Enterprises | 359,873 |  | 318,565 |  | 338,425 |
Results of Operations, Production or Lifting Costs | 140,606 |  | 127,403 |  | 123,148 |
Results of Operations, Depreciation, Depletion and Amortization, and Valuation Provisions | 139,539 | [1] | 127,266 | [1] | 126,278 | [1]
Results of Operations, Impairment of Oil and Gas Properties | 0 |  | 0 |  | 620,000 |
Results of Operations, Income before Income Taxes | 173,441 |  | 179,680 |  | (429,771) |
Income Tax Expense (Benefit) | 63,655 |  | 66,293 |  | (164,216) |
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs) | 109,786 |  | 113,387 |  | (265,555) |
Accretion of discount for asset retirement obligations oil and gas | $ 3,600 |  | $ 3,200 |  | $ 2,700 |
[1] | Includes accretion of discount for asset retirement obligations of $3.6 million, $3.2 million and $2.7 million for the years ended December 31, 2011, 2010 and 2009, respectively, as discussed in Note 10.

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