Income Taxes (Reconciliation of the Provision for Income Taxes to the Amounts Computed at the Federal Statutory Rate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal income taxes at statutory rate	$ 355,758	$ 573,231	$ 573,020
State income taxes, net of federal tax benefit	56,345	39,062	35,285
Excess tax benefit from share-based compensation	(34,703)	(48,688)	0
Revaluation of deferred tax liability	(1,262)	(53,240)	0
Other items, net	(6,538)	(6,365)	(8,805)
Provision for income taxes	$ 369,600	$ 504,000	$ 599,500