Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
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