v3.26.3
Municipal Bond Guarantee Reinsurance - Narrative (Details)
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Jul. 01, 2024
Guarantor Obligations [Line Items]            
Member surplus contributions, insurance premium charges, percentage 55.00%   55.00%      
Assets held-in-trust $ 992,600,000   $ 992,600,000   $ 1,006,500,000  
Collateral trusts, investments and cash 313,700,000   313,700,000   323,300,000  
Surplus notes 271,500,000   271,500,000   276,800,000  
Interest receivable 6,700,000   6,700,000   7,000,000.0  
Debt 928,600,000   928,600,000   837,000,000.0  
Interest income from BAM Surplus Notes 6,800,000 $ 7,500,000 20,600,000 $ 22,500,000    
Change in fair value of BAM Surplus Notes (16,100,000)   (16,100,000) 0    
BAM Surplus Notes            
Guarantor Obligations [Line Items]            
Distribution received 13,500,000 15,400,000 42,300,000 37,600,000    
Accrued interest 6,900,000 7,500,000 20,900,000 22,700,000    
Cash distribution received 6,600,000 7,900,000 21,400,000 14,900,000    
BAM Surplus Notes | Surplus Notes            
Guarantor Obligations [Line Items]            
Stated margin           10.00%
Net release of cash (pre-funding) of investment purchases 8,000,000.0 8,000,000.0 8,000,000.0 8,000,000.0    
Repayment of principal 5,300,000 5,600,000 5,300,000 5,600,000    
Accrued interest payment held in trust 100,000 100,000 100,000 100,000    
Accrued interest payment held outside of trust 2,600,000 2,300,000 2,600,000 2,300,000    
Debt 271,500,000   271,500,000   276,800,000  
Interest receivable $ 231,600,000   $ 231,600,000   $ 213,700,000  
BAM Surplus Notes | Surplus Notes | Discount Rate            
Guarantor Obligations [Line Items]            
Debt instrument, measurement input 0.0900   0.0900   0.0805  
HG Global            
Guarantor Obligations [Line Items]            
Premiums written, gross $ 19,300,000 15,900,000 $ 38,600,000 41,800,000    
Assumed Premiums Earned 8,600,000 7,500,000 24,000,000.0 22,800,000    
HG Global | Operating Segments            
Guarantor Obligations [Line Items]            
Debt 197,400,000   197,400,000   $ 147,800,000  
Interest income from BAM Surplus Notes 6,800,000 7,500,000 20,600,000 22,500,000    
Notes receivable, fair value disclosure 335,500,000 396,200,000 335,500,000 396,200,000 339,000,000.0  
Change in fair value of BAM Surplus Notes (16,100,000) 0 (16,100,000) 0    
Payments of principal and interest $ (8,000,000.0) $ (8,000,000.0) (8,000,000.0) $ (8,000,000.0)    
Subsidiary - HG Global            
Guarantor Obligations [Line Items]            
Purchase of surplus notes     $ 503,000,000.0      
Percentage of risk premium ceded 60.00%   60.00%      
Renegotiation period     5 years      
Percent over a target trust balance     102.00%      
Subsidiary - HG Global | Regulation 114            
Guarantor Obligations [Line Items]            
Assets held-in-trust $ 400,700,000   $ 400,700,000   399,400,000  
Supplement trust target 603,000,000.0   603,000,000.0      
Subsidiary - HG Global | Supplemental Trust            
Guarantor Obligations [Line Items]            
Assets held-in-trust $ 591,900,000   $ 591,900,000   $ 607,100,000  
Subsidiary - HG Global | Maximum            
Guarantor Obligations [Line Items]            
Percentage of par value of policy reinsured 15.00%   15.00%      
Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd.            
Guarantor Obligations [Line Items]            
Reinsured amount     $ 125,000,000.0