Reinsurance - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Reinsurance Retention Policy
Ceded Premiums Earned	$ 75,523,000	$ 93,829,000
Catastrophe Excess of Loss
Reinsurance Retention Policy
Retension loss events	100,000,000
Third event retention level	3,750,000
First event retention level	29,750,000
Second event retention level	18,500,000
Catastrophe Excess of Loss | Shoreline Re
Reinsurance Retention Policy
First event retention level	15,750,000
Subsequent event retention level	$ 4,500,000
Quota Share Agreement | 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-217-year
Reinsurance, excess retention, amount reinsured, per policy	$ 1,676,000,000
Event retention level	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	0.50%
Program provides sufficient coverage return period	1-in-227-year
Reinsurance, excess retention, amount reinsured, per policy	$ 170,400,000
Reinsurance, excess retention level per event	95,600,000
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
Reinsurance, aggregate retention	$ 40,000,000