Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,934	$ 3,090	$ 6,310	$ 6,310
Interest cost	7,069	7,269	14,449	14,450
Expected return on assets	(10,307)	(9,167)	(21,005)	(18,326)
Amortization of prior service cost	53	52	105	104
Amortization of net actuarial loss	2,193	1,830	4,427	3,430
Total pension expense	1,942	3,074	4,286	5,968
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	670	633	1,341	1,283
Interest cost	1,682	1,713	3,365	3,388
Expected return on assets	(2,796)	(2,771)	(5,592)	(5,550)
Amortization of net actuarial loss	214	0	428	0
Total pension expense	$ (230)	$ (425)	$ (458)	$ (879)