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Investments - Additional Information (Detail) $ in Millions | Dec. 31, 2018 USD ($) Security | Dec. 31, 2017 USD ($) Security
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Investments Debt And Equity Securities [Abstract] |  |
Available-for-sale, investment securities held with maturity dates more than one year and less than two years | $ | $ 31.8 | $ 48.7
Number of securities in unrealized loss position | Security | 57 | 54

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- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- References No definition available. + Details
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