Income Taxes (Reconciliation of the Provision for Income Taxes to the Amounts Computed at the Federal Statutory Rate) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred Income Taxes and Tax Credits [Abstract]
Federal, current	$ 348,303	$ 311,631	$ 228,443
Federal, deferred	847	10,030	55,175
Federal, total	349,150	321,661	283,618
State, current	38,428	35,982	25,537
State, deferred	1,072	(1,868)	(1,055)
State, total	39,500	34,114	24,482
Current income tax expense (benefit)	386,731	347,613	253,980
Deferred income tax expense (benefit)	1,919	8,162	54,120
Provision for income taxes	$ 388,650	$ 355,775	$ 308,100