Income Taxes (Schedule of Components of the Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Federal income tax expense, current	$ 289,953	$ 467,577	$ 540,090
Federal income tax expense (benefit), deferred	16,309	(13,053)	7,558
Federal income tax expense, total	306,262	454,524	547,648
State income tax expense, current	59,487	41,183	49,016
State income tax expense (benefit), deferred	3,851	8,293	2,836
State income tax expense, total	63,338	49,476	51,852
Current income tax expense	349,440	508,760	589,106
Deferred income tax expense (benefit)	20,160	(4,760)	10,394
Provision for income taxes	$ 369,600	$ 504,000	$ 599,500