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