Employee Benefit Plans (Components Of Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
BancShares Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 3,362	$ 2,934	$ 6,791	$ 6,310
Interest cost	7,131	7,069	14,188	14,449
Expected return on assets	(11,976)	(10,307)	(23,933)	(21,005)
Amortization of prior service cost	20	53	40	105
Amortization of net actuarial loss	3,548	2,193	6,794	4,427
Total pension expense	2,085	1,942	3,880	4,286
Bancorporation Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	624	670	1,286	1,341
Interest cost	1,592	1,682	3,179	3,365
Expected return on assets	(3,110)	(2,796)	(6,216)	(5,592)
Amortization of net actuarial loss	86	214	157	428
Total pension expense	$ (808)	$ (230)	$ (1,594)	$ (458)