Employee Benefit Plans (Funded Status Of Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions	$ 50,000	$ 30,000
BancShares Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	611,502	627,645
Service cost	12,618	14,083	$ 12,332
Interest cost	28,892	26,975	25,615
Actuarial (gain) loss	40,571	(39,002)
Benefits paid	(20,356)	(18,199)
Benefit obligation at December 31	673,227	611,502	627,645
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	550,025	544,956
Actual return on plan assets	20,947	(6,732)
Employer contributions	50,000	30,000
Benefits paid	(20,356)	(18,199)
Fair value of plan assets, ending balance	600,616	550,025	544,956
Funded status	(72,611)	(61,477)
Bancorporation Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Curtailments	0	(2,076)	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	143,241	151,332
Service cost	2,567	3,341	832
Interest cost	6,775	6,393	1,488
Actuarial (gain) loss	9,682	(10,937)
Benefits paid	(5,434)	(4,812)
Benefit obligation at December 31	156,831	143,241	151,332
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	150,893	155,618
Actual return on plan assets	6,625	87
Benefits paid	(5,434)	(4,812)
Fair value of plan assets, ending balance	152,084	150,893	$ 155,618
Funded status	$ (4,747)	$ 7,652