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Securities (Realized Gains and Losses) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Proceeds from sales, available-for-sale debt securities | $ 223,763 | $ 42,085 | $ 375,102 | $ 256,875
Gross realized gains, available-for-sale debt securities | 1,447 | 210 | 3,008 | 2,339
Related tax expense, available-for-sale debt securities | $ 428 | $ 62 | $ 889 | $ 690

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