Fair Values of Financial Instruments - Schedule of Assets Measured at Amortized Cost Net of Allowance For Credit Losses (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	$ 371,355	$ 399,721
States and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	339,371	356,268
Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	21,147	32,670
U.S. Agency-Based Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	2,480	2,643
U.S. Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	8,348	8,127
Asset-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	9	13
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	8,348	8,127
Fair Value, Inputs, Level 1 [Member] \| U.S. Treasury Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	8,348	8,127
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	363,007	391,594
Fair Value, Inputs, Level 2 [Member] \| States and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	339,371	356,268
Fair Value, Inputs, Level 2 [Member] \| Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	21,147	32,670
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]
Securities held-to-maturity-fixed maturity, Fair Value	2,480	2,643
Fair Value, Inputs, Level 2 [Member] \| Asset-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities held-to-maturity-fixed maturity, Fair Value	$ 9	$ 13

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]