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Securities - Additional Information (Details)
3 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2019
USD ($)
Tranche
institution
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Debt Securities, Available-for-sale [Line Items]        
Proceeds from sales of securities available for sale   $ 212,485,000 $ 2,387,000 $ 495,340,000
Debt securities, AFS, realized gain (loss)   348,000 (16,000) 148,000
Amortized Cost   1,276,871,000 1,264,529,000  
Securities available for sale, at fair value   $ 1,290,613,000 1,250,777,000  
Number of securities representing interests in tranches of trusts (tranches) | Tranche   2    
Number of institutions issuing debt (institutions) | institution   148    
Trust preferred securities        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost   $ 12,153,000 12,359,000  
Securities available for sale, at fair value   9,986,000 10,633,000  
Other than temporary impairment losses   0 0 0
Secure government, public and trust deposits        
Debt Securities, Available-for-sale [Line Items]        
Debt securities, AFS, restricted   416,849,000 619,308,000  
Short-term borrowings        
Debt Securities, Available-for-sale [Line Items]        
Debt securities, AFS, restricted   $ 27,754,000 $ 18,299,000  
Durbin Amendment Securities        
Debt Securities, Available-for-sale [Line Items]        
Carrying Value $ 446,880,000     $ 446,880,000
Proceeds from sales of securities available for sale 446,971,000      
Debt securities, AFS, realized gain (loss) $ 91,000