Employee Benefit Plans (Funded Status Of Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Bancorporation Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	$ 169,480	$ 156,831
Service cost	2,572	2,548	$ 2,567
Interest cost	6,357	6,653	6,775
Actuarial (gain) loss	(10,268)	9,168
Benefits paid	(6,081)	(5,720)
Benefit obligation at December 31	162,060	169,480	156,831
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	168,591	152,084
Actual return on plan assets	(11,443)	22,227
Fair value of plan assets, ending balance	151,067	168,591	152,084
Funded status	(10,993)	(889)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	6,081	5,720
BancShares Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	749,948	673,227
Service cost	13,582	12,638	12,618
Interest cost	28,376	28,940	28,892
Actuarial (gain) loss	(77,484)	57,041
Benefits paid	(23,507)	(21,898)
Benefit obligation at December 31	690,915	749,948	673,227
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	712,999	600,616
Actual return on plan assets	(48,025)	84,281
Employer contributions	50,000	50,000
Fair value of plan assets, ending balance	691,467	712,999	$ 600,616
Funded status	552	(36,949)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ 23,507	$ 21,898