Loans and Allowance for Credit Losses (Disaggregation of Credit Quality Disclosures) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	$ 3,188,870
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,912,012
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,669,888
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,581,704
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,268,121
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,830,813
Revolving Loans	2,484,822
Revolving Loans Converted to Term Loans	120,412
Notes Receivable Gross	17,056,642	$ 17,267,424
Total Commercial [Member] | Pass [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	3,105,699
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,786,344
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,522,262
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,519,030
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,168,590
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,700,798
Revolving Loans	2,374,150
Revolving Loans Converted to Term Loans	106,518
Notes Receivable Gross	16,283,391	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	35,706
Term Loans, Amortized Cost Basis by Origination Year, 2020	65,397
Term Loans, Amortized Cost Basis by Origination Year, 2019	93,299
Term Loans, Amortized Cost Basis by Origination Year, 2018	32,980
Term Loans, Amortized Cost Basis by Origination Year, 2017	39,412
Term Loans, Amortized Cost Basis by Origination Year, Prior	94,821
Revolving Loans	75,154
Revolving Loans Converted to Term Loans	6,880
Notes Receivable Gross	443,649	541,885
Total Commercial [Member] | Special Mention [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	13,328
Term Loans, Amortized Cost Basis by Origination Year, 2020	2,734
Term Loans, Amortized Cost Basis by Origination Year, 2019	7,601
Term Loans, Amortized Cost Basis by Origination Year, 2018	11,757
Term Loans, Amortized Cost Basis by Origination Year, 2017	15,009
Term Loans, Amortized Cost Basis by Origination Year, Prior	9,447
Revolving Loans	13,030
Revolving Loans Converted to Term Loans	2,184
Notes Receivable Gross	75,090	137,592
Total Commercial [Member] | Substandard [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	34,137
Term Loans, Amortized Cost Basis by Origination Year, 2020	57,537
Term Loans, Amortized Cost Basis by Origination Year, 2019	46,726
Term Loans, Amortized Cost Basis by Origination Year, 2018	17,937
Term Loans, Amortized Cost Basis by Origination Year, 2017	45,110
Term Loans, Amortized Cost Basis by Origination Year, Prior	25,747
Revolving Loans	22,488
Revolving Loans Converted to Term Loans	4,830
Notes Receivable Gross	254,512	255,045
Residential Mortgage and Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	238,737
Term Loans, Amortized Cost Basis by Origination Year, 2020	431,147
Term Loans, Amortized Cost Basis by Origination Year, 2019	436,321
Term Loans, Amortized Cost Basis by Origination Year, 2018	319,522
Term Loans, Amortized Cost Basis by Origination Year, 2017	426,564
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,094,153
Revolving Loans	1,137,614
Revolving Loans Converted to Term Loans	7,830
Notes Receivable Gross	4,091,888	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	238,432
Term Loans, Amortized Cost Basis by Origination Year, 2020	429,863
Term Loans, Amortized Cost Basis by Origination Year, 2019	433,925
Term Loans, Amortized Cost Basis by Origination Year, 2018	314,469
Term Loans, Amortized Cost Basis by Origination Year, 2017	417,118
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,063,622
Revolving Loans	1,135,616
Revolving Loans Converted to Term Loans	6,421
Notes Receivable Gross	4,039,466	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	305
Term Loans, Amortized Cost Basis by Origination Year, 2020	1,284
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,396
Term Loans, Amortized Cost Basis by Origination Year, 2018	5,053
Term Loans, Amortized Cost Basis by Origination Year, 2017	9,446
Term Loans, Amortized Cost Basis by Origination Year, Prior	30,531
Revolving Loans	1,998
Revolving Loans Converted to Term Loans	1,409
Notes Receivable Gross	$ 52,422	$ 67,200