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Investment Securities (Narrative) (Details)
 12 Months Ended
Dec. 31, 2019
USD ($)
Security
Dec. 31, 2018
USD ($)
Security
Dec. 31, 2017
USD ($)
Investments [Abstract]      
Securities pledged as collateral $ 676,900,000 $ 751,000,000  
Number of security positions, unrealized loss position | Security 91 571  
Number of security positions, unrealized loss position for more than 12 months | Security 34 435  
Securities, 12 months or longer, Fair Value $ 47,202,000 $ 672,797,000  
Securities, 12 months or longer, Unrealized Losses $ 659,000 $ 18,467,000  
Number of security positions, unrealized loss position for less than 12 months | Security 57 136  
Securities, less than 12 months, Fair Value $ 178,723,000 $ 50,770,000  
Securities, less than 12 months, Unrealized Losses 1,595,000 182,000  
Impairment recorded $ 0 $ 0 $ 0