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Investments - Additional Information (Detail) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) Security | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) Security | Sep. 30, 2017 USD ($)
Investments Schedule [Abstract] |  |  |  |
Individual fixed maturity held in unrealized loss position | Security | 507 |  | 507 |
Individual fixed maturity held in unrealized loss position longer than 12 months | Security | 101 |  | 101 |
Net unrealized gains on equity securities | $ 573,000 |  | $ 259,000 |
Impairment losses recognized |  |  | 0 | $ 0
Net realized losses on investments | $ (329,000) | $ (192,000) | (1,471,000) | $ (761,000)
Sale of equity and fixed maturity securities classified as available-for-sale |  |  | 1,100,000 |
Net realized losses on fixed maturity securities |  |  | $ 400,000 |

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- Definition Amount of realized loss on 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 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562 + Details
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