Loans and Allowance for Credit Losses (Disaggregation of Credit Quality Disclosures) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	$ 1,839,140
Term Loans, Amortized Cost Basis by Origination Year, 2020	5,046,749
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,868,200
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,711,606
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,363,394
Term Loans, Amortized Cost Basis by Origination Year, Prior	2,075,690
Revolving Loans	2,481,137
Revolving Loans Converted to Term Loans	33,699
Notes Receivable Gross	17,419,615	$ 17,267,424
Total Commercial [Member] | Pass [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	1,785,609
Term Loans, Amortized Cost Basis by Origination Year, 2020	4,899,613
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,713,484
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,641,419
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,257,878
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,928,878
Revolving Loans	2,353,884
Revolving Loans Converted to Term Loans	28,649
Notes Receivable Gross	16,609,414	16,332,902
Total Commercial [Member] | Pass-Watch [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	28,339
Term Loans, Amortized Cost Basis by Origination Year, 2020	70,487
Term Loans, Amortized Cost Basis by Origination Year, 2019	88,986
Term Loans, Amortized Cost Basis by Origination Year, 2018	45,747
Term Loans, Amortized Cost Basis by Origination Year, 2017	42,878
Term Loans, Amortized Cost Basis by Origination Year, Prior	102,659
Revolving Loans	79,774
Revolving Loans Converted to Term Loans	3,716
Notes Receivable Gross	462,586	541,885
Total Commercial [Member] | Special Mention [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	15,621
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,150
Term Loans, Amortized Cost Basis by Origination Year, 2019	24,326
Term Loans, Amortized Cost Basis by Origination Year, 2018	4,087
Term Loans, Amortized Cost Basis by Origination Year, 2017	15,110
Term Loans, Amortized Cost Basis by Origination Year, Prior	9,743
Revolving Loans	13,567
Revolving Loans Converted to Term Loans	550
Notes Receivable Gross	86,154	137,592
Total Commercial [Member] | Substandard [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	9,571
Term Loans, Amortized Cost Basis by Origination Year, 2020	73,499
Term Loans, Amortized Cost Basis by Origination Year, 2019	41,404
Term Loans, Amortized Cost Basis by Origination Year, 2018	20,353
Term Loans, Amortized Cost Basis by Origination Year, 2017	47,528
Term Loans, Amortized Cost Basis by Origination Year, Prior	34,410
Revolving Loans	33,912
Revolving Loans Converted to Term Loans	784
Notes Receivable Gross	261,461	255,045
Residential Mortgage and Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	106,799
Term Loans, Amortized Cost Basis by Origination Year, 2020	412,682
Term Loans, Amortized Cost Basis by Origination Year, 2019	470,245
Term Loans, Amortized Cost Basis by Origination Year, 2018	375,515
Term Loans, Amortized Cost Basis by Origination Year, 2017	499,733
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,218,170
Revolving Loans	1,157,910
Revolving Loans Converted to Term Loans	4,190
Notes Receivable Gross	4,245,244	4,522,507
Residential Mortgage and Consumer [Member] | Performing [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	106,606
Term Loans, Amortized Cost Basis by Origination Year, 2020	410,414
Term Loans, Amortized Cost Basis by Origination Year, 2019	465,522
Term Loans, Amortized Cost Basis by Origination Year, 2018	369,198
Term Loans, Amortized Cost Basis by Origination Year, 2017	489,147
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,179,718
Revolving Loans	1,154,507
Revolving Loans Converted to Term Loans	4,138
Notes Receivable Gross	4,179,250	4,455,307
Residential Mortgage and Consumer [Member] | Nonperforming [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	193
Term Loans, Amortized Cost Basis by Origination Year, 2020	2,268
Term Loans, Amortized Cost Basis by Origination Year, 2019	4,723
Term Loans, Amortized Cost Basis by Origination Year, 2018	6,317
Term Loans, Amortized Cost Basis by Origination Year, 2017	10,586
Term Loans, Amortized Cost Basis by Origination Year, Prior	38,452
Revolving Loans	3,403
Revolving Loans Converted to Term Loans	52
Notes Receivable Gross	$ 65,994	$ 67,200