Loans And Allowance For Loan Losses (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Loans And Allowance For Loan Losses [Abstract]
Loans pledged at the Federal Home Loan Bank as collateral for borrowings and letters of credit obtained to secure public deposits	$ 3,700,000,000
Loans Pledged to the Federal Reserve Bank as collateral for discount window borrowings	$ 1,700,000,000
Period after which loans are deemed in default (in days)	90 days
Effect on Interest Income Resulting From Modification to Credit Card Loans	$ (896,000)
Commitments to lend additional funds to customers with restructured loans	10,600,000
Fair Value of Personal Real Estate Loans Held for Sale	6,500,000
Unpaid Principal Balance on Personal Real Estate Loans Held for Sale	6,300,000
Student Loans Held for Sale, Lower of Cost or Fair Value	10,000,000
HFS Loans on non accrual status	0
HFS loans past due and still accruing	0
Foreclosed real estate	1,300,000	$ 681,000
Personal property acquired in repossession	$ 3,100,000	$ 2,700,000