Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,628	$ 3,396	$ 7,886	$ 10,187
Interest cost	7,557	7,093	22,669	21,281
Expected return on assets	(12,876)	(11,966)	(38,629)	(35,899)
Amortization of prior service cost	15	19	43	59
Amortization of net actuarial loss	2,099	3,398	6,297	10,192
Total pension expense	(577)	1,940	(1,734)	5,820
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	563	643	1,689	1,929
Interest cost	1,759	1,588	5,276	4,767
Expected return on assets	(2,771)	(3,106)	(8,314)	(9,322)
Amortization of net actuarial loss	631	78	1,895	235
Total pension expense	$ 182	$ (797)	$ 546	$ (2,391)