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Securities - Additional Information (Detail) $ in Thousands | Sep. 30, 2018 USD ($) Security | Dec. 31, 2017 USD ($)
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Investments Debt And Equity Securities [Abstract] |  |
Carrying value of pledged securities | $ | $ 124,687 | $ 122,862
Number of securities in portfolio with unrealized losses | Security | 185 |

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- Definition Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729 + Details
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