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Company's Invested Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | $ 1,226,309 | $ 1,293,793
Equity securities | 17,045 | 16,508
U.S. Treasuries |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 544,543 | 494,223
Obligations of States and Political Subdivisions |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 23,092 | 26,150
Mortgage Backed Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 57,542 | 58,927
Commercial Mortgage-Backed Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 77,771 | 79,080
Asset-backed Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 199,695 | 202,952
Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 224,664 | 291,713
Foreign Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 99,002 | 140,748
Fair Value, Measurements, Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 1,226,309 | 1,293,793
Equity securities | 17,045 | 16,508
Total invested assets | 1,243,354 | 1,310,301
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 | 544,543 | 494,223
Equity securities | 0 | 0
Total invested assets | 544,543 | 494,223
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 | 681,766 | 799,570
Equity securities | 17,045 | 16,508
Total invested assets | 698,811 | 816,078
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 | 0 | 0
Equity securities | 0 | 0
Total invested assets | 0 | 0
Fair Value, Measurements, Recurring | U.S. Treasuries |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 544,543 | 494,223
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 | 544,543 | 494,223
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 | Obligations of States and Political Subdivisions |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 23,092 | 26,150
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 | 23,092 | 26,150
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 | 57,542 | 58,927
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 | 57,542 | 58,927
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 | 0 | 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 | 77,771 | 79,080
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 | 77,771 | 79,080
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 | 199,695 | 202,952
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 | 199,695 | 202,952
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 | 0 | 0
Fair Value, Measurements, Recurring | Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 224,664 | 291,713
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 | 224,664 | 291,713
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 | 0 | 0
Fair Value, Measurements, Recurring | Foreign Corporate Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total invested assets | 99,002 | 140,748
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 | 99,002 | 140,748
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

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