Loans and Allowance for Credit Losses (Disaggregation of Credit Quality Disclosures) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	$ 3,999,639
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,447,115
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,425,787
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,434,200
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,175,313
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,633,575
Revolving Loans	2,667,146
Revolving Loans Converted to Term Loans	129,071
Notes Receivable Gross	16,911,846	$ 17,267,424
Total Commercial [Member] | Pass [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	3,916,476
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,333,009
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,308,701
Term Loans, Amortized Cost Basis by Origination Year, 2018	1,374,599
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,105,917
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,520,061
Revolving Loans	2,582,321
Revolving Loans Converted to Term Loans	105,856
Notes Receivable Gross	16,246,940	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	40,835
Term Loans, Amortized Cost Basis by Origination Year, 2020	59,789
Term Loans, Amortized Cost Basis by Origination Year, 2019	71,484
Term Loans, Amortized Cost Basis by Origination Year, 2018	31,238
Term Loans, Amortized Cost Basis by Origination Year, 2017	22,528
Term Loans, Amortized Cost Basis by Origination Year, Prior	82,569
Revolving Loans	47,600
Revolving Loans Converted to Term Loans	15,253
Notes Receivable Gross	371,296	541,885
Total Commercial [Member] | Special Mention [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	15,346
Term Loans, Amortized Cost Basis by Origination Year, 2020	3,105
Term Loans, Amortized Cost Basis by Origination Year, 2019	6,857
Term Loans, Amortized Cost Basis by Origination Year, 2018	11,061
Term Loans, Amortized Cost Basis by Origination Year, 2017	19,648
Term Loans, Amortized Cost Basis by Origination Year, Prior	8,613
Revolving Loans	11,841
Revolving Loans Converted to Term Loans	1,296
Notes Receivable Gross	77,767	137,592
Total Commercial [Member] | Substandard [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	26,982
Term Loans, Amortized Cost Basis by Origination Year, 2020	51,212
Term Loans, Amortized Cost Basis by Origination Year, 2019	38,745
Term Loans, Amortized Cost Basis by Origination Year, 2018	17,302
Term Loans, Amortized Cost Basis by Origination Year, 2017	27,220
Term Loans, Amortized Cost Basis by Origination Year, Prior	22,332
Revolving Loans	25,384
Revolving Loans Converted to Term Loans	6,666
Notes Receivable Gross	215,843	255,045
Residential Mortgage and Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2021	330,749
Term Loans, Amortized Cost Basis by Origination Year, 2020	462,370
Term Loans, Amortized Cost Basis by Origination Year, 2019	403,676
Term Loans, Amortized Cost Basis by Origination Year, 2018	269,386
Term Loans, Amortized Cost Basis by Origination Year, 2017	372,720
Term Loans, Amortized Cost Basis by Origination Year, Prior	998,690
Revolving Loans	1,129,472
Revolving Loans Converted to Term Loans	7,106
Notes Receivable Gross	3,974,169	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	330,316
Term Loans, Amortized Cost Basis by Origination Year, 2020	461,269
Term Loans, Amortized Cost Basis by Origination Year, 2019	401,774
Term Loans, Amortized Cost Basis by Origination Year, 2018	265,787
Term Loans, Amortized Cost Basis by Origination Year, 2017	367,106
Term Loans, Amortized Cost Basis by Origination Year, Prior	973,576
Revolving Loans	1,128,048
Revolving Loans Converted to Term Loans	5,619
Notes Receivable Gross	3,933,495	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	433
Term Loans, Amortized Cost Basis by Origination Year, 2020	1,101
Term Loans, Amortized Cost Basis by Origination Year, 2019	1,902
Term Loans, Amortized Cost Basis by Origination Year, 2018	3,599
Term Loans, Amortized Cost Basis by Origination Year, 2017	5,614
Term Loans, Amortized Cost Basis by Origination Year, Prior	25,114
Revolving Loans	1,424
Revolving Loans Converted to Term Loans	1,487
Notes Receivable Gross	$ 40,674	$ 67,200