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Securities - Additional Information (Details) $ in Thousands | Mar. 31, 2018 USD ($) security | Jan. 01, 2018 USD ($) | Dec. 31, 2017 USD ($) security
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Number of debt securities in unrealized loss position | security |  | 71 |  | 51
Securities pledged for regulatory and legal requirements |  | $ 221,000 |  | $ 249,000
Accounting Standards Update 2016-01 | AOCI |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Net unrealized gains and losses, net of tax, reclassified from AOCI to retained earnings on marketable equity securities | [1] |  | $ (862) |
Accounting Standards Update 2016-01 | Retained Earnings |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Net unrealized gains and losses, net of tax, reclassified from AOCI to retained earnings on marketable equity securities | [1] |  | $ 862 |
[1] | Reclassification due to the adoption of ASU No. 2016-01

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