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Securities Available-for-Sale - Amortized Cost and Fair Value of Available-for-Sale Securities (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | $ 695,284 |  | $ 686,205
Fair Value | 698,291 |  | 693,487
Obligations of U.S. government corporations and agencies |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Due in one year or less, Amortized Cost | 58,501 |  |
Due after one year through five years, Amortized Cost | 141,646 |  |
Due after five years through ten years, Amortized Cost | 70,584 |  |
Due after ten years, Amortized Cost | 34,416 |  |
Available-for-sale Securities, Debt Maturities, Amortized Cost | 305,147 |  |
Due in one year or less, Fair Value | 58,438 |  |
Due after one year through five years, Fair Value | 142,859 |  |
Due after five years through ten years, Fair Value | 72,132 |  |
Due after ten years, Fair Value | 35,955 |  |
Fair Value, Debt securities | 309,384 |  |
Collateralized mortgage obligations of U.S. government corporations and agencies |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 109,916 |  | 130,046
Fair Value | 108,688 |  | 129,777
Residential mortgage-backed securities of U.S. government corporations and agencies |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 32,388 |  | 36,606
Fair Value | 32,854 |  | 37,358
Commercial mortgage-backed securities of U.S. government corporations and agencies |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 244,018 | [1] | 127,311
Fair Value | 242,221 | [1] | 125,604
Debt Securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 691,469 |  | 678,626
Fair Value | 693,147 |  | 682,238
Marketable equity securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized Cost | 3,815 |  | 7,579
Fair Value | $ 5,144 |  | $ 11,249
[1] | Includes a $5.9 million security purchase that was pending settlement as of December 31, 2017.

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