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Reinsurance - Additional Information (Details) - USD ($)
 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Jun. 30, 2024
Jun. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Reinsurance Retention Policy            
Ceded Premiums Earned $ 81,939,000 $ 85,692,000     $ 262,785,000 $ 275,400,000
Reinsurance Contract [Axis]: XOL Commutation            
Reinsurance Retention Policy            
Ceded Premiums Earned     $ 6,300,000 $ 15,700,000    
Catastrophe Excess of Loss            
Reinsurance Retention Policy            
Retension loss events 100,000,000       100,000,000  
Third event retention level 3,750,000       3,750,000  
First event retention level 29,750,000       29,750,000  
Second event retention level 18,500,000       $ 18,500,000  
Quota Share Agreement | Shoreline Re            
Reinsurance Retention Policy            
Cession Rate         45.00%  
Quota Share Agreement | Reinsurance Contract [Axis]: 06/01/2024 - 06/01/2026 | Shoreline Re            
Reinsurance Retention Policy            
Cession Rate         30.00%  
Quota Share Agreement | Reinsurance Contract [Axis]: 06/01/2025 - 06/01/2026 | Shoreline Re            
Reinsurance Retention Policy            
Cession Rate         45.00%  
American Coastal Insurance Company | Catastrophe Excess of Loss            
Reinsurance Retention Policy            
Insured long term debt project demand decrease         $ 69,000,000,000  
Program provides sufficient coverage period         1-in-100-year  
Percentage of singe occurrence exceeding protection purchased         0.50%  
Program provides sufficient coverage return period         1-in-203-year  
Reinsurance, excess retention, amount reinsured, per policy         $ 1,676,000,000  
Event retention level 14,000,000       14,000,000  
Reinsurance, excess retention, amount reinsured, per event         $ 1,330,000,000  
American Coastal Insurance Company | Catastrophe Excess of Loss | Maximum            
Reinsurance Retention Policy            
Program provides sufficient coverage probability rate         0.10%  
American Coastal Insurance Company | All Other Perilds Catastrophe Excess of Loss            
Reinsurance Retention Policy            
Percentage of singe occurrence exceeding protection purchased         0.20%  
Program provides sufficient coverage return period         1-in-450-year  
Reinsurance, excess retention, amount reinsured, per policy         $ 176,400,000  
Reinsurance, excess retention level per event 88,200,000       88,200,000  
American Coastal Insurance Company | Catastrophe Aggregate Excess of Loss            
Reinsurance Retention Policy            
Reinsurance, excess retention, amount reinsured, per policy         40,000,000  
Event occurrence limit 20,000,000       20,000,000  
Reinsurance, aggregate retention         40,000,000  
UPC Re | Catastrophe Excess of Loss            
Reinsurance Retention Policy            
First event retention level 15,750,000       15,750,000  
Subsequent event retention level $ 4,500,000       $ 4,500,000