Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,568	$ 3,429
Interest cost	7,531	7,057
Expected return on assets	(12,867)	(11,957)
Amortization of prior service cost	14	20
Amortization of net actuarial loss	2,114	3,246
Total pension expense	(640)	1,795
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	545	662
Interest cost	1,760	1,587
Expected return on assets	(2,768)	(3,106)
Amortization of net actuarial loss	627	71
Total pension expense	$ 164	$ (786)