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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Cumulative effect on retained earnings $ (1,085,975,000) $ (1,045,478,000) $ (999,877,000)  
Accrued interest receivable 65,547,000 36,781,000    
Allowance for loan and lease losses 204,809,000 116,539,000 164,231,000  
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Transfers Net $ 0 0 0  
Other Intangible Assets [Member] | Minimum [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Finite lived intangible asset, useful life 3 years      
Other Intangible Assets [Member] | Maximum [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Finite lived intangible asset, useful life 10 years      
COVID-19 Deferral Program Loans [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Accrued interest receivable $ 35,400,000      
Allowance for loan and lease losses 711,000      
Interest receivable, current status 30,500,000      
Retained Earnings [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Cumulative effect on retained earnings (300,096,000) (279,646,000) (253,040,000) $ (200,878,000)
Accounting Standards Update 2016-13 [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Accrued interest receivable on loans $ 64,500,000 32,700,000    
Accounting Standards Update 2016-13 [Member] | Retained Earnings [Member] | Cumulative Effect, Period Of Adoption, Adjustment [Member]        
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]        
Cumulative effect on retained earnings   $ 25,494,000 $ 0 $ 0