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Document & Entity Information - shares
 9 Months Ended
Sep. 30, 2025
Nov. 03, 2025
Document and Entity Information [Abstract]    
Entity Incorporation, State or Country Code DE  
Entity Address, Address Line One 570 Carillon Parkway, Suite 100  
Document Type 10-Q  
Document Quarterly Report true  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q3  
Document Fiscal Year Focus 2025  
Trading Symbol ACIC  
Title of 12(b) Security Common Stock, $0.0001 par value per share  
Security Exchange Name NASDAQ  
Registrant Name American Coastal Insurance Corporation  
City Area Code 727  
Local Phone Number 633-0851  
Central Index Key 0001401521  
Filer Category Accelerated Filer  
Common Stock, Shares, Outstanding   48,765,302
Document Transition Report false  
Entity File Number 001-35761  
Entity Emerging Growth Company false  
Entity Interactive Data Current Yes  
Entity Shell Company false  
Entity Small Business false  
Entity Current Reporting Status Yes  
Entity Address, City or Town St. Petersburg  
Entity Address, State or Province FL  
Entity Tax Identification Number 75-3241967  
Entity Address, Postal Zip Code 33716  
Document Period End Date Sep. 30, 2025