Loans and Allowance for Credit Losses (Disaggregation of Credit Quality Disclosures) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	$ 1,272,817
Term Loans, Amortized Cost Basis by Origination Year, 2019	3,633,698
Term Loans, Amortized Cost Basis by Origination Year, 2018	2,478,292
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,948,787
Term Loans, Amortized Cost Basis by Origination Year, 2016	1,345,235
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,930,274
Revolving Loans	3,711,322
Revolving Loans Converted to Term Loans	63,744
Notes Receivable Gross	16,384,169	$ 16,057,306
Total Commercial [Member] | Pass [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	1,200,289
Term Loans, Amortized Cost Basis by Origination Year, 2019	3,482,650
Term Loans, Amortized Cost Basis by Origination Year, 2018	2,316,675
Term Loans, Amortized Cost Basis by Origination Year, 2017	1,817,884
Term Loans, Amortized Cost Basis by Origination Year, 2016	1,268,500
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,815,527
Revolving Loans	3,166,739
Revolving Loans Converted to Term Loans	40,805
Notes Receivable Gross	15,109,069	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	45,483
Term Loans, Amortized Cost Basis by Origination Year, 2019	89,492
Term Loans, Amortized Cost Basis by Origination Year, 2018	50,169
Term Loans, Amortized Cost Basis by Origination Year, 2017	73,719
Term Loans, Amortized Cost Basis by Origination Year, 2016	45,264
Term Loans, Amortized Cost Basis by Origination Year, Prior	45,098
Revolving Loans	393,676
Revolving Loans Converted to Term Loans	2,068
Notes Receivable Gross	744,969	462,502
Total Commercial [Member] | Special Mention [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	1,106
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,754
Term Loans, Amortized Cost Basis by Origination Year, 2018	11,838
Term Loans, Amortized Cost Basis by Origination Year, 2017	26,324
Term Loans, Amortized Cost Basis by Origination Year, 2016	699
Term Loans, Amortized Cost Basis by Origination Year, Prior	20,130
Revolving Loans	21,204
Revolving Loans Converted to Term Loans	1,319
Notes Receivable Gross	85,374	101,583
Total Commercial [Member] | Substandard [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	25,939
Term Loans, Amortized Cost Basis by Origination Year, 2019	58,802
Term Loans, Amortized Cost Basis by Origination Year, 2018	86,630
Term Loans, Amortized Cost Basis by Origination Year, 2017	30,860
Term Loans, Amortized Cost Basis by Origination Year, 2016	30,772
Term Loans, Amortized Cost Basis by Origination Year, Prior	49,519
Revolving Loans	127,734
Revolving Loans Converted to Term Loans	19,552
Notes Receivable Gross	429,808	479,110
Total Commercial [Member] | Doubtful [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2018	12,980
Revolving Loans	1,969
Notes Receivable Gross	14,949
Residential Mortgage and Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Term Loans, Amortized Cost Basis by Origination Year, 2020	172,950
Term Loans, Amortized Cost Basis by Origination Year, 2019	530,795
Term Loans, Amortized Cost Basis by Origination Year, 2018	581,487
Term Loans, Amortized Cost Basis by Origination Year, 2017	778,524
Term Loans, Amortized Cost Basis by Origination Year, 2016	626,671
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,137,938
Revolving Loans	1,297,415
Revolving Loans Converted to Term Loans	5,732
Notes Receivable Gross	5,131,512	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	172,403
Term Loans, Amortized Cost Basis by Origination Year, 2019	528,274
Term Loans, Amortized Cost Basis by Origination Year, 2018	577,525
Term Loans, Amortized Cost Basis by Origination Year, 2017	771,724
Term Loans, Amortized Cost Basis by Origination Year, 2016	622,557
Term Loans, Amortized Cost Basis by Origination Year, Prior	1,096,363
Revolving Loans	1,295,598
Revolving Loans Converted to Term Loans	4,256
Notes Receivable Gross	5,068,700	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	547
Term Loans, Amortized Cost Basis by Origination Year, 2019	2,521
Term Loans, Amortized Cost Basis by Origination Year, 2018	3,962
Term Loans, Amortized Cost Basis by Origination Year, 2017	6,800
Term Loans, Amortized Cost Basis by Origination Year, 2016	4,114
Term Loans, Amortized Cost Basis by Origination Year, Prior	41,575
Revolving Loans	1,817
Revolving Loans Converted to Term Loans	1,476
Notes Receivable Gross	$ 62,812	$ 57,283