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Securities - Additional Information (Detail) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items] |  |
Investments with a carrying value | $ 84.5 | $ 129.4
Minimum [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Underwater security | 10 years |
Loss position existed | 3 years |

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- Definition Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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=64858031&loc=SL6224234-111729 + Details
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