Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 3,429	$ 3,376
Interest cost	7,057	7,380
Expected return on assets	(11,957)	(10,698)
Amortization of prior service cost	20	52
Amortization of net actuarial loss	3,246	2,234
Total pension expense	1,795	2,344
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	662	671
Interest cost	1,587	1,683
Expected return on assets	(3,106)	(2,796)
Amortization of net actuarial loss	71	214
Total pension expense	$ (786)	$ (228)