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Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | $ 315,114 | $ 317,064
Equity securities, at fair value (cost $36,020 and $44,046 in 2024 and 2023, respectively) | 57,712 | 57,147
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 315,114 | 317,064
Total | 372,826 | 374,211
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 14,067 | 13,671
Total | 71,779 | 70,818
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 301,047 | 303,393
Total | 301,047 | 303,393
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 143,607 | 131,895
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 143,607 | 131,895
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 153,079 | 166,753
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 153,079 | 166,753
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] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 4,361 | 4,745
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 4,361 | 4,745
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 14,067 | 13,671
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $318,495 allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 14,067 | 13,671
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost $36,020 and $44,046 in 2024 and 2023, respectively) | 57,712 | 57,147
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost $36,020 and $44,046 in 2024 and 2023, respectively) | $ 57,712 | $ 57,147

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