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, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of provision for income taxes
Federal income taxes at statutory rate	$ 474,681	$ 375,942	$ 355,758
State income taxes, net of federal tax benefit	76,810	54,739	56,345
Excess tax benefit from share-based compensation	(16,918)	(25,992)	(34,703)
Revaluation of deferred tax liability	0	0	(1,262)
Benefit from investment in renewable energy tax credits	(17,904)	(875)	(2,037)
Other items, net	(2,566)	(4,527)	(4,501)
Provision for income taxes	$ 514,103	$ 399,287	$ 369,600