Income Taxes (Reconciliation of Provision (Benefit) for Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Income Taxes
Expected provision (benefit) at federal statutory rate	$ (402,571)		$ 367,854		$ 348,632
Increase (decrease) resulting from:
State income taxes, net of federal income tax effect	(44,454)		40,145		39,975
Nondeductible expenses	2,100		1,244		660
Other	1,786		3,978		2,392
Provision (benefit) for income taxes	$ (443,139)	[1]	$ 413,221	[1]	$ 391,659	[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.