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, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Interest Cost        
Interest costs charged to expense $ 49,728 $ 72,770 $ 95,902 $ 149,742
Interest costs capitalized 8,038 8,128 16,008 16,082
Total interest costs incurred 57,766 80,898 111,910 165,824
Interest Costs (Textual) [Abstract]        
Non cash interest expense included in interest costs $ 5,490 $ 10,384 $ 10,932 $ 21,031