Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 3,180	$ 3,153	$ 9,490	$ 9,463
Interest cost	7,283	7,218	21,732	21,668
Expected return on assets	(10,589)	(9,155)	(31,594)	(27,481)
Amortization of prior service cost	53	54	158	158
Amortization of net actuarial loss	2,214	1,714	6,641	5,144
Total pension expense	2,141	2,984	6,427	8,952
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	569	642	1,910	1,925
Interest cost	1,624	1,694	4,989	5,081
Expected return on assets	(2,783)	(2,775)	(8,375)	(8,325)
Amortization of net actuarial loss	63	0	491	0
Total pension expense	$ (527)	$ (439)	$ (985)	$ (1,319)