v3.26.3
Investments Available-for-Sale Securities in a Loss Position (Details)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
security
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value $ 3,838,105   $ 3,838,105   $ 686,671
Less than 12 months, gross unrealized holding losses 170,496   170,496   2,059
12 Months or Longer, Estimated Fair Value 348,524   348,524   637,608
12 Months or Longer, Gross Unrealized Holding Losses 69,526   69,526   84,437
Total Estimated Fair Value 4,186,629   4,186,629   1,324,279
Total Gross Unrealized Holding Losses 240,022   240,022   86,496
Beginning balance 56 $ 42 29 $ 27  
Increase to allowance from securities for which credit losses were not previously recorded 0 0 43 0  
Reduction from securities sold during the period 0 0 (16) (14)  
Net increase (decrease) from securities that had an allowance at the beginning of the period (1) (4) (1) 25  
Ending balance 55 $ 38 $ 55 $ 38  
Debt Securities Available For Sale Allowance For Credit Loss Number Of Securities | security     5    
U.S. Treasury securities and obligations of U.S. government agencies          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 838   $ 838   296
Less than 12 months, gross unrealized holding losses 31   31   1
12 Months or Longer, Estimated Fair Value 0   0   0
12 Months or Longer, Gross Unrealized Holding Losses 0   0   0
Total Estimated Fair Value 838   838   296
Total Gross Unrealized Holding Losses 31   31   1
Beginning balance     0    
Ending balance 0   0    
Obligations of states, municipalities and political subdivisions [Member]          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 5,845   5,845   1,043
Less than 12 months, gross unrealized holding losses 373   373   2
12 Months or Longer, Estimated Fair Value 71,145   71,145   118,027
12 Months or Longer, Gross Unrealized Holding Losses 22,221   22,221   18,408
Total Estimated Fair Value 76,990   76,990   119,070
Total Gross Unrealized Holding Losses 22,594   22,594   18,410
Beginning balance     3    
Ending balance 2   2    
Corporate and other securities [Member]          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 1,583,369   1,583,369   101,385
Less than 12 months, gross unrealized holding losses 71,291   71,291   597
12 Months or Longer, Estimated Fair Value 126,838   126,838   239,152
12 Months or Longer, Gross Unrealized Holding Losses 27,802   27,802   25,635
Total Estimated Fair Value 1,710,207   1,710,207   340,537
Total Gross Unrealized Holding Losses 99,093   99,093   26,232
Beginning balance     26    
Ending balance 53   53    
Asset-backed securities [Member]          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 346,029   346,029   92,682
Less than 12 months, gross unrealized holding losses 6,888   6,888   384
12 Months or Longer, Estimated Fair Value 7,918   7,918   7,759
12 Months or Longer, Gross Unrealized Holding Losses 421   421   254
Total Estimated Fair Value 353,947   353,947   100,441
Total Gross Unrealized Holding Losses 7,309   7,309   638
Beginning balance     0    
Ending balance 0   0    
Residential mortgage-backed securities [Member]          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 1,539,055   1,539,055   387,397
Less than 12 months, gross unrealized holding losses 82,866   82,866   779
12 Months or Longer, Estimated Fair Value 85,930   85,930   228,531
12 Months or Longer, Gross Unrealized Holding Losses 16,499   16,499   37,971
Total Estimated Fair Value 1,624,985   1,624,985   615,928
Total Gross Unrealized Holding Losses 99,365   99,365   38,750
Beginning balance     0    
Ending balance 0   0    
Commercial mortgage-backed securities          
Debt Securities, Available-for-sale [Line Items]          
Less than 12 Months, Estimated Fair Value 362,969   362,969   103,868
Less than 12 months, gross unrealized holding losses 9,047   9,047   296
12 Months or Longer, Estimated Fair Value 56,693   56,693   44,139
12 Months or Longer, Gross Unrealized Holding Losses 2,583   2,583   2,169
Total Estimated Fair Value 419,662   419,662   148,007
Total Gross Unrealized Holding Losses 11,630   11,630   $ 2,465
Beginning balance     0    
Ending balance $ 0   $ 0