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Investment Securities Available For Sale - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]      
Proceeds from sales of investment securities $ 107,100,000 $ 208,200,000 $ 99,200,000
Net gains (losses) from sales of investment securities $ (100,000) $ (2,300,000) 2,100,000
Contractual maturities (up to) 30 years    
Available for sale securities portfolio, weighted average life 7 years 47 days 4 years 106 days  
Other-than-temporary impairment loss $ 0 $ 0 $ 0