Income Taxes (Schedule of Components of the Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Federal income tax expense, current	$ 504,558	$ 399,271	$ 348,303
Federal income tax expense (benefit), deferred	(21,973)	5,987	847
Federal income tax expense, total	482,585	405,258	349,150
State income tax expense, current	47,242	43,242	38,428
State income tax expense (benefit), deferred	(677)	(4,500)	1,072
State income tax expense, total	46,565	38,742	39,500
Current income tax expense	551,800	442,513	386,731
Deferred income tax expense (benefit)	(22,650)	1,487	1,919
Provision for income taxes	$ 529,150	$ 444,000	$ 388,650