Loans and Allowance for Credit Losses (Composition of Nonaccrual Loans and Without an Allowance for Loan Loss by Portfolio Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	$ 108,434	$ 139,879
Nonaccrual without allowance for loan loss	19,663	25,127
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	4,818	6,743
Nonaccrual without allowance for loan loss	4,273
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	1,689	2,486
Nonaccrual without allowance for loan loss		1,116
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	40,715	40,573
Nonaccrual without allowance for loan loss	1,603	1,705
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	21,758	23,385
Total Commercial And Industrial [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	39,454	66,692
Nonaccrual without allowance for loan loss	13,787	22,306
Total Commercial And Industrial [Member] | Total Commercial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	27,650	52,836
Nonaccrual without allowance for loan loss	6,841	15,268
Total Commercial And Industrial [Member] | Total Commercial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Nonaccrual	11,804	13,856
Nonaccrual without allowance for loan loss	$ 6,946	$ 7,038