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Investment Securities (Narrative) (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
Security
Dec. 31, 2017
USD ($)
Security
Dec. 31, 2016
USD ($)
Investments [Abstract]      
Securities pledged as collateral $ 751,000,000 $ 838,400,000  
Number of security positions, unrealized loss position | Security 571 411  
Number of security positions, unrealized loss position for more than 12 months | Security 435 172  
Securities, 12 months or longer, Fair Value $ 672,797,000 $ 274,763,000  
Securities, 12 months or longer, Unrealized Losses $ 18,467,000 $ 7,033,000  
Number of security positions, unrealized loss position for less than 12 months | Security 136 239  
Securities, less than 12 months, Fair Value $ 50,770,000 $ 433,097,000  
Securities, less than 12 months, Unrealized Losses 182,000 3,957,000  
Impairment recorded $ 0 $ 0 $ 0