| **Assets Held for Sale, Divestitures and Discontinued Operations (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Discontinued Operations and Disposal Groups [Abstract]**                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| Schedule of Discontinued Operations                                         | Selected financial information related to divested and discontinued operations.The tables below set forth selected financial information related to net assets held for sale and operating results related to discontinued operations. Net assets held for sale represents the assets that are expected to be sold, net of liabilities that are expected to be assumed by the purchaser. While the reclassification of revenues and expenses related to discontinued operations for the prior period had no impact upon previously reported net earnings, the statement of operations table presents the revenues and expenses that were reclassified from the specified statement of operations line items to discontinued operations. The following table presents balance sheet data related to assets held for sale as of March 31, 2013:Balance Sheet Net Assets Held for Sale  (in thousands)Assets  Properties and equipment $782,556Accumulated depreciation, depletion and amortization (565,754)Total Assets $216,802   Liabilities  Asset retirement obligation $28,346   Net Assets $188,456       The following table presents statement of operations data related to our discontinued operations:  Three Months Ended Statements of Operations - Discontinued Operations 2013 2012  (in thousands)Revenues    Natural gas, NGLs and crude oil sales $10,274 $12,811Sales from natural gas marketing 450 453Well operations, pipeline income and other 450 566Total revenues 11,174 13,830     Costs, expenses and other    Production costs 5,393 7,102Cost of natural gas marketing 454 401Depreciation, depletion and amortization 2,258 11,902Other 495 348Gain on sale of properties and equipment — (20,335)Total costs, expenses and other 8,600 (582)     Income from discontinued operations 2,574 14,412Provision for income taxes (1,037) (5,341)Income from discontinued operations, net of tax $1,537 $9,071      |

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| - Definition
Tabular disclosure of disposal groups, which may include the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations, the classification and carrying value of the assets and liabilities comprising the disposal group, and the segment in which the disposal group was reported. Also may include the amount of adjustments to amounts previously reported in discontinued operations such as resolution of contingencies arising from the disposal transaction or the operations of the component prior to disposal.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1474-107760Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2443-110228Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 43, 44, 45, 47, 48 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1510-107760
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