Income Taxes (Schedule Of Statutory Federal Income Tax Rate Reconciles To Actual Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Income tax expense (benefit) at statutory federal rate	$ 246,718	$ 158,151	$ 217,498
State income taxes, net	14,668	10,443	19,652
Other nondeductible expenses	3,149	3,205	2,949
Nontaxable income	(24,688)	(20,397)	(17,869)
Tax credits and other taxes	(1,704)	(2,926)	(1,717)
Other	(2,285)	(6,088)	2,448
Income Tax Expense (Benefit), Total	$ 235,858	$ 142,388	$ 222,961