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Asset Retirement Obligation (Details Textual) (USD $) | Mar. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2008
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Asset Retirement Obligations [Line Items] |  |  |  |  |
Asset retirement obligation | $ 8,302,000 | $ 8,882,000 | $ 9,594,000 | $ 9,679,000 |
Asset Retirement Obligation (Textual) [Abstract] |  |  |  |  |
Fair value of asset retirement obligations related to the legal requirements |  |  |  |  | 11,500,000
Other current liabilities [Member] |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |
Asset retirement obligation |  | 3,600,000 |  |  |
Other Long Term Liabilities [Member] |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |
Asset retirement obligation | $ 3,000,000 |  |  |  |

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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 3, 10, 22 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Definition Carrying amount of an asset that is legally restricted for purposes of settling an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph b -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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