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Investments - Additional Information (Detail) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2020 USD ($) Security | Mar. 31, 2019 USD ($) | Dec. 31, 2019 USD ($)
Marketable Securities [Line Items] |  |  |
Individual fixed maturity held in unrealized loss position | Security | 20 |  |
Individual fixed maturity held in unrealized loss position longer than 12 months | Security | 0 |  |
Number of fixed maturity securities, allowance for credit loss | Security | 419 |  |
Fixed maturity securities, allowance for credit loss | $ 275,000 |  | $ 0
Fixed maturity securities, available-for-sale, allowance for credit losses | 0 |  | $ 0
Net realized gains | 1,000,000.0 |  |
Net unrealized gains (losses) on equity securities | (8,763,000) | $ 2,158,000 |
Corporate Bonds [Member] |  |  |
Marketable Securities [Line Items] |  |  |
Fixed maturity securities, allowance for credit loss | $ 215,000 |  |
Number of majority securities | Security | 48 |  |
States and Political Subdivisions [Member] |  |  |
Marketable Securities [Line Items] |  |  |
Fixed maturity securities, allowance for credit loss | $ 50,000 |  |
Number of majority securities | Security | 368 |  |
Corporate Fixed Income Securities [Member] | Maximum [Member] |  |  |
Marketable Securities [Line Items] |  |  |
Investments maturity period using default rate | 20 years |  |

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- Definition Amount of allowance for credit 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 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922900-210455 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aaa) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 + Details
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