Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 3,396	$ 3,180	$ 10,187	$ 9,490
Interest cost	7,093	7,283	21,281	21,732
Expected return on assets	(11,966)	(10,589)	(35,899)	(31,594)
Amortization of prior service cost	19	53	59	158
Amortization of net actuarial loss	3,398	2,214	10,192	6,641
Total pension expense	1,940	2,141	5,820	6,427
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	643	569	1,929	1,910
Interest cost	1,588	1,624	4,767	4,989
Expected return on assets	(3,106)	(2,783)	(9,322)	(8,375)
Amortization of net actuarial loss	78	63	235	491
Total pension expense	$ (797)	$ (527)	$ (2,391)	$ (985)