Income Taxes (Schedule of Effective Tax Rate Reconciliation) (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income tax provision calculated using the federal statutory income tax rate	$ 299,900	$ 323,416	$ 167,674
State income taxes, net of federal income tax benefit	30,955	29,555	13,087
Effect of statutory rate change	(429)	(578)	11,502
Other	1,071	(1,681)	1,280
Total income tax expense	$ 331,497	$ 350,712	$ 193,543