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Fair Values of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | $ 478,730 | $ 465,594
Equity securities, Fair Value | 18,651 | 9,282
Total |  | 474,876
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 478,730 | 465,594
Total | 497,381 | 474,876
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, Fair Value | 18,651 | 9,282
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 233,245 | 251,140
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 173,214 | 130,222
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 12,515 | 18,014
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 59,756 | 66,218
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 59,756 | 66,218
Total | 78,407 | 75,466
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stock [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, Fair Value | 18,651 | 9,248
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 59,756 | 66,218
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 418,974 | 399,376
Total | 418,974 | 399,376
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | States and Political Subdivisions [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 233,245 | 251,140
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bonds [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | 173,214 | 130,222
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Available-for-sale—fixed maturity, Fair Value | $ 12,515 | 18,014
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total |  | 34
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stock [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, Fair Value |  | $ 34

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