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Investments - Additional Information (Detail) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2020 USD ($) Security | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) Security | Jun. 30, 2019 USD ($) | Dec. 31, 2019 USD ($)
Marketable Securities [Line Items] |  |  |  |  |
Individual fixed maturity held in unrealized loss position | Security | 2 |  | 2 |  |
Individual fixed maturity held in unrealized loss position longer than 12 months | Security | 0 |  | 0 |  |
Number of fixed maturity securities, allowance for credit loss | Security | 390 |  | 390 |  |
Fixed maturity securities, allowance for credit loss | $ 357,000 |  | $ 357,000 |  | $ 0
Fixed maturity securities, available-for-sale, allowance for credit losses | 0 |  | 0 |  | $ 0
Net realized gains (losses) | 200,000 | $ (100,000) | 1,200,000 |  |
Net unrealized gains (losses) on equity securities | 5,570,000 | $ 642,000 | (3,193,000) | $ 2,800,000 |
Corporate Bonds [Member] |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Fixed maturity securities, allowance for credit loss | $ 299,000 |  | $ 299,000 |  |
Number of majority securities | Security | 32 |  | 32 |  |
States and Political Subdivisions [Member] |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Fixed maturity securities, allowance for credit loss | $ 49,000 |  | $ 49,000 |  |
Number of majority securities | Security | 355 |  | 355 |  |
Corporate Fixed Income Securities [Member] | Maximum [Member] |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |
Investments maturity period using default rate |  |  | 20 years |  |

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