Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,690	$ 3,362	$ 5,258	$ 6,791
Interest cost	7,581	7,131	15,112	14,188
Expected return on assets	(12,886)	(11,976)	(25,753)	(23,933)
Amortization of prior service cost	14	20	28	40
Amortization of net actuarial loss	2,084	3,548	4,198	6,794
Total pension expense	(517)	2,085	(1,157)	3,880
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	581	624	1,126	1,286
Interest cost	1,757	1,592	3,517	3,179
Expected return on assets	(2,775)	(3,110)	(5,543)	(6,216)
Amortization of net actuarial loss	637	86	1,264	157
Total pension expense	$ 200	$ (808)	$ 364	$ (1,594)