v3.26.1
Fair Values of Financial Instruments - Schedule of Assets Measured at Amortized Cost Net of Allowance For Credit Losses (Detail) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Securities held-to-maturity-fixed maturity, Fair Value $ 332,659 $ 344,576
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 306,351 317,529
Corporate Bonds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Securities held-to-maturity-fixed maturity, Fair Value 15,653 16,245
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 2,238 2,348
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 8,408 8,445
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 9
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 8,408 8,445
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 8,408 8,445
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 324,251 336,131
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 306,351 317,529
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 15,653 16,245
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 2,238 2,348
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 $ 9