Income Taxes (Reconciliation of Provision for Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Income Taxes
Expected provision (benefit) at federal statutory rate	$ 367,854		$ 348,632		$ (18,205)
Increase (decrease) resulting from:
State income taxes, net of federal income tax effect	40,145		39,975		415
Non-deductible expenses	1,244		660		1,497
Other	3,978		2,392		(70)
Provision (benefit) for income taxes	$ 413,221	[1]	$ 391,659	[1]	$ (16,363)

[1] (1) Interest income, interest expense and the provision (benefit) for income taxes by segment are an allocation of corporate amounts as cash equivalents, debt and income tax expense allocated as they are incurred at the corporate level.