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           Interest Costs (Details) (USD $) 
        In Thousands, unless otherwise specified  | 
        3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
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           Sep. 30, 2012 
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           Sep. 30, 2011 
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           Sep. 30, 2012 
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           Sep. 30, 2011 
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| Interest Cost | ||||
| Interest costs charged to expense | $ 70,035 | $ 75,316 | $ 219,777 | $ 229,730 | 
| Interest costs capitalized | 8,005 | 8,906 | 24,087 | 24,224 | 
| Total interest costs incurred | 78,040 | 84,222 | 243,864 | 253,954 | 
| Interest Costs (Textual) [Abstract] | ||||
| Non cash interest expense included in interest costs | $ 9,755 | $ 9,977 | $ 30,786 | $ 29,211 | 
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- Definition 
          Amount of interest costs capitalized disclosed as an adjusting item to interest costs incurred. No definition available. 
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- Definition 
          Total interest costs incurred during the period and either capitalized or charged against earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          The cost of borrowed funds accounted for as interest that was charged against earnings during the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Interest paid other than in cash for example by issuing additional debt securities. As a noncash item, it is added to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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