Employee Benefit Plans (Funded Status Of Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions	$ 30,000
BancShares Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	627,645	$ 530,678
Service cost	14,083	12,332	$ 16,332
Interest cost	26,975	25,615	23,686
Actuarial (gain) loss	(39,002)	76,122
Benefits paid	(18,199)	(17,102)
Benefit obligation at December 31	611,502	627,645	530,678
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	544,956	524,017
Actual return on plan assets	(6,732)	38,041
Employer contributions	30,000	0
Benefits paid	(18,199)	(17,102)
Fair value of plan assets, ending balance	550,025	544,956	524,017
Funded status	(61,477)	(82,689)
Bancorporation Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Curtailments	(2,076)	0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	151,332	137,452
Service cost	3,341	832
Interest cost	6,393	1,488
Actuarial (gain) loss	(10,937)	12,802
Benefits paid	(4,812)	(1,242)
Benefit obligation at December 31	143,241	151,332	137,452
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	155,618	0
Actual return on plan assets	87	6,486
Benefits paid	(4,812)	(1,242)
Fair value of plan assets, ending balance	150,893	155,618	$ 0
Funded status	$ 7,652	$ 4,286