Company's Invested Assets and Derivative Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	$ 1,248,198	$ 1,201,866
Equity securities	17,520	99,978
U.S. Treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	344,103	150,118
Agency Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets		5,630
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	31,595	54,721
Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	62,116	250,341
Commercial Mortgage-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	98,664	136,893
Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	189,400	172,642
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	338,780	292,383
Foreign Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	183,540	139,138
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	1,248,198	1,201,866
Equity securities	17,520	99,978
Total invested assets	1,265,718	1,301,844
Total invested liabilities		8,395
Fair Value, Measurements, Recurring | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested liabilities		8,395
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	344,103	150,118
Equity securities	0	75,750
Total invested assets	344,103	225,868
Total invested liabilities		0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested liabilities		0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	900,795	1,049,216
Equity securities	16,249	23,991
Total invested assets	917,044	1,073,207
Total invested liabilities		8,395
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested liabilities		8,395
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	3,300	2,532
Equity securities	1,271	237
Total invested assets	4,571	2,769
Total invested liabilities		0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested liabilities		0
Fair Value, Measurements, Recurring | U.S. Treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	344,103	150,118
Fair Value, Measurements, Recurring | U.S. Treasuries | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	344,103	150,118
Fair Value, Measurements, Recurring | U.S. Treasuries | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | U.S. Treasuries | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Agency Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets		5,630
Fair Value, Measurements, Recurring | Agency Obligations | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets		0
Fair Value, Measurements, Recurring | Agency Obligations | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets		5,630
Fair Value, Measurements, Recurring | Agency Obligations | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets		0
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	31,595	54,721
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	31,595	54,721
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	62,116	250,341
Fair Value, Measurements, Recurring | Mortgage Backed Securities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Mortgage Backed Securities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	61,156	250,341
Fair Value, Measurements, Recurring | Mortgage Backed Securities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	960	0
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	98,664	136,893
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	98,664	136,893
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed Securities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	189,400	172,642
Fair Value, Measurements, Recurring | Asset-backed Securities | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Asset-backed Securities | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	189,073	171,686
Fair Value, Measurements, Recurring | Asset-backed Securities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	327	956
Fair Value, Measurements, Recurring | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	338,780	292,383
Fair Value, Measurements, Recurring | Corporate Bonds | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Corporate Bonds | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	336,767	290,807
Fair Value, Measurements, Recurring | Corporate Bonds | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	2,013	1,576
Fair Value, Measurements, Recurring | Foreign Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	183,540	139,138
Fair Value, Measurements, Recurring | Foreign Corporate Bonds | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	0	0
Fair Value, Measurements, Recurring | Foreign Corporate Bonds | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	183,540	139,138
Fair Value, Measurements, Recurring | Foreign Corporate Bonds | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total invested assets	$ 0	$ 0