v3.26.1
Investments - Schedule of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Jun. 30, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 17,940,189 $ 17,589,342  
Percentage of total 100.00% 100.00%  
U.S. Government direct, guaranteed, and government-sponsored enterprises      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 386,964 $ 383,853  
States, municipalities, and political subdivisions      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 2,968,024 2,880,626  
Foreign governments      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 39,001 39,546  
Corporates      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 14,400,162 14,171,518  
Corporates | Industrials      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 7,471,921 7,317,686  
Corporates | Financial      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 4,777,087 4,782,326  
Corporates | Utilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 2,151,154 2,071,506  
Corporates | Other corporate sectors      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 7,471,921    
Other asset-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 146,038 113,799  
Quoted Prices in Active Markets for Identical Assets (Level 1)      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 0 $ 0  
Percentage of total 0.00% 0.00%  
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government direct, guaranteed, and government-sponsored enterprises      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 0 $ 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | States, municipalities, and political subdivisions      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign governments      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporates      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporates | Industrials      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value   0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporates | Financial      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporates | Utilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporates | Other corporate sectors      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0    
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other asset-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 0 0  
Significant Other Observable Inputs (Level 2)      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 17,467,607 $ 17,194,117  
Percentage of total 97.00% 98.00%  
Significant Other Observable Inputs (Level 2) | U.S. Government direct, guaranteed, and government-sponsored enterprises      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 386,964 $ 383,853  
Significant Other Observable Inputs (Level 2) | States, municipalities, and political subdivisions      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 2,965,047 2,880,626  
Significant Other Observable Inputs (Level 2) | Foreign governments      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 39,001 39,546  
Significant Other Observable Inputs (Level 2) | Corporates      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 14,060,533 13,862,194  
Significant Other Observable Inputs (Level 2) | Corporates | Industrials      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value   7,232,179  
Significant Other Observable Inputs (Level 2) | Corporates | Financial      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 4,648,035 4,661,175  
Significant Other Observable Inputs (Level 2) | Corporates | Utilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 2,018,134 1,968,840  
Significant Other Observable Inputs (Level 2) | Corporates | Other corporate sectors      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 7,394,364    
Significant Other Observable Inputs (Level 2) | Other asset-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 16,062 27,898  
Significant Unobservable Inputs (Level 3)      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 472,582 $ 395,225  
Percentage of total 3.00% 2.00% 3.00%
Significant Unobservable Inputs (Level 3) | U.S. Government direct, guaranteed, and government-sponsored enterprises      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 0 $ 0  
Significant Unobservable Inputs (Level 3) | States, municipalities, and political subdivisions      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 2,977 0  
Percentage of total 0.00%   0.00%
Significant Unobservable Inputs (Level 3) | Foreign governments      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 0 0  
Significant Unobservable Inputs (Level 3) | Corporates      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 339,629 309,324  
Percentage of total 2.00%   3.00%
Significant Unobservable Inputs (Level 3) | Corporates | Industrials      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value   85,507  
Significant Unobservable Inputs (Level 3) | Corporates | Financial      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 129,052 121,151  
Significant Unobservable Inputs (Level 3) | Corporates | Utilities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 133,020 102,666  
Significant Unobservable Inputs (Level 3) | Corporates | Other corporate sectors      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value 77,557    
Significant Unobservable Inputs (Level 3) | Other asset-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Value $ 129,976 $ 85,901