Income Taxes (Schedule of Components of the Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Federal income tax expense, current	$ 540,090	$ 504,558	$ 399,271
Federal income tax expense (benefit), deferred	7,558	(21,973)	5,987
Federal income tax expense, total	547,648	482,585	405,258
State income tax expense, current	49,016	47,242	43,242
State income tax expense (benefit), deferred	2,836	(677)	(4,500)
State income tax expense, total	51,852	46,565	38,742
Current income tax expense	589,106	551,800	442,513
Deferred income tax expense (benefit)	10,394	(22,650)	1,487
Provision for income taxes	$ 599,500	$ 529,150	$ 444,000