Quarterly report pursuant to Section 13 or 15(d)

Interest Costs (Details)

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Interest Costs (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Interest Cost        
Interest costs charged to expense $ 72,770 $ 76,196 $ 149,742 $ 154,414
Interest costs capitalized 8,128 8,068 16,082 15,318
Total interest costs incurred 80,898 84,264 165,824 169,732
Interest Costs (Textual) [Abstract]        
Non cash interest expense included in interest costs $ 10,384 $ 9,661 $ 21,031 $ 19,234