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Asset Retirement Obligation (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2012
Asset Retirement Obligation [Abstract] |
Asset retirement obligations description | Due to the high rate of lease renewals over a long period of time, the calculation assumes that all related assets will be removed at some period over the next 50 years.

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- Definition A general description of the asset retirement obligations and the associated long-lived assets. Description may include the terms of the legal restriction. + 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Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 (a) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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