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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 |  |  |

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