v3.26.1
Cover - shares
6 Months Ended
Jun. 30, 2026
Aug. 11, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-42695  
Registrant Name ATEGRITY SPECIALTY INSURANCE COMPANY HOLDINGS  
Entity Incorporation, State or Country Code NV  
Entity Tax Identification Number 82-4925734  
Entity Address, Address Line One 9 West 57th Street  
Entity Address, Address Line Two 33rd Floor  
Entity Address, City or Town New York  
Entity Address, State or Province NY  
Entity Address, Postal Zip Code 10019  
City Area Code (212)  
Local Phone Number 509-1600  
Title of 12(b) Security Common stock, par value $0.001 per share  
Trading Symbol ASIC  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   47,926,928
Entity Central Index Key 0002040491  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Amendment Flag false