Loans and Allowance for Credit Losses (Disaggregation of Credit Quality Disclosures) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	$ 4,383,632
Term Loans, Amortized Cost Basis by Origination Year, 2019	3,422,279
Term Loans, Amortized Cost Basis by Origination Year, 2018	2,272,688
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,800,876
Term Loans, Amortized Cost Basis by Origination Year, 2016	1,265,588
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,750,203
Revolving Loans	2,684,222
Revolving Loans Converted to Term Loans	127,309
Notes Receivable Gross	17,706,797	$ 16,057,306
Total Commercial [Member] | Pass [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	4,296,564
Term Loans, Amortized Cost Basis by Origination Year, 2019	3,327,755
Term Loans, Amortized Cost Basis by Origination Year, 2018	2,146,064
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,672,980
Term Loans, Amortized Cost Basis by Origination Year, 2016	1,187,467
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,605,845
Revolving Loans	2,518,581
Revolving Loans Converted to Term Loans	100,625
Notes Receivable Gross	16,855,881	15,014,111
Total Commercial [Member] | Pass-Watch [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	52,823
Term Loans, Amortized Cost Basis by Origination Year, 2019	53,406
Term Loans, Amortized Cost Basis by Origination Year, 2018	64,528
Term Loans, Amortized Cost Basis by Origination Year, 2017	86,433
Term Loans, Amortized Cost Basis by Origination Year, 2016	45,023
Term Loans, Amortized Cost Basis by Origination Year, Prior	85,315
Revolving Loans	102,437
Revolving Loans Converted to Term Loans	12,810
Notes Receivable Gross	502,775	462,502
Total Commercial [Member] | Special Mention [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	1,598
Term Loans, Amortized Cost Basis by Origination Year, 2019	4,372
Term Loans, Amortized Cost Basis by Origination Year, 2018	5,798
Term Loans, Amortized Cost Basis by Origination Year, 2017	26,179
Term Loans, Amortized Cost Basis by Origination Year, 2016	13,687
Term Loans, Amortized Cost Basis by Origination Year, Prior	16,091
Revolving Loans	11,882
Revolving Loans Converted to Term Loans	1,242
Notes Receivable Gross	80,849	101,583
Total Commercial [Member] | Substandard [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	32,647
Term Loans, Amortized Cost Basis by Origination Year, 2019	36,746
Term Loans, Amortized Cost Basis by Origination Year, 2018	56,298
Term Loans, Amortized Cost Basis by Origination Year, 2017	15,284
Term Loans, Amortized Cost Basis by Origination Year, 2016	19,411
Term Loans, Amortized Cost Basis by Origination Year, Prior	42,952
Revolving Loans	51,322
Revolving Loans Converted to Term Loans	12,632
Notes Receivable Gross	267,292	479,110
Residential Mortgage and Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	278,488
Term Loans, Amortized Cost Basis by Origination Year, 2019	510,452
Term Loans, Amortized Cost Basis by Origination Year, 2018	537,913
Term Loans, Amortized Cost Basis by Origination Year, 2017	709,193
Term Loans, Amortized Cost Basis by Origination Year, 2016	589,269
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,040,807
Revolving Loans	1,245,995
Revolving Loans Converted to Term Loans	9,463
Notes Receivable Gross	4,921,580	5,155,449
Residential Mortgage and Consumer [Member] | Performing [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	277,534
Term Loans, Amortized Cost Basis by Origination Year, 2019	506,177
Term Loans, Amortized Cost Basis by Origination Year, 2018	531,553
Term Loans, Amortized Cost Basis by Origination Year, 2017	698,878
Term Loans, Amortized Cost Basis by Origination Year, 2016	583,723
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,004,835
Revolving Loans	1,242,586
Revolving Loans Converted to Term Loans	5,459
Notes Receivable Gross	4,850,745	5,098,166
Residential Mortgage and Consumer [Member] | Nonperforming [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	954
Term Loans, Amortized Cost Basis by Origination Year, 2019	4,275
Term Loans, Amortized Cost Basis by Origination Year, 2018	6,360
Term Loans, Amortized Cost Basis by Origination Year, 2017	10,315
Term Loans, Amortized Cost Basis by Origination Year, 2016	5,546
Term Loans, Amortized Cost Basis by Origination Year, Prior	35,972
Revolving Loans	3,409
Revolving Loans Converted to Term Loans	4,004
Notes Receivable Gross	$ 70,835	$ 57,283