XML 20 R1.htm IDEA: XBRL DOCUMENT v3.25.4
Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 02, 2026
Jun. 30, 2025
Apr. 30, 2013
Entity Information [Line Items]        
Document Type 10-K      
Document Quarterly Report true      
Document Period End Date Dec. 31, 2025      
Entity File Number 1-10777      
Entity Registrant Name OCTAVE SPECIALTY GROUP, INC.      
Entity Incorporation, State or Country Code DE      
Entity Tax Identification Number 13-3621676      
Entity Address, Address Line One 40 Wall Street      
Entity Address, City or Town New York      
Entity Address, State or Province NY      
Entity Address, Postal Zip Code 10005      
City Area Code (212)      
Local Phone Number 658-7470      
Title of 12(b) Security Common Stock, par value $0.01 per share      
Trading Symbol OSG      
Security Exchange Name NYSE      
Entity Current Reporting Status Yes      
Entity Interactive Data Current Yes      
Entity Filer Category Accelerated Filer      
Entity Small Business false      
Document Transition Report false      
Entity Emerging Growth Company false      
Entity Shell Company false      
Entity Common Stock, Shares Outstanding   44,951,913    
Common stock, par value (in dollars per share)       $ 0.01
Amendment Flag false      
Document Fiscal Year Focus 2025      
Document Fiscal Period Focus FY      
Entity Central Index Key 0000874501      
Current Fiscal Year End Date --12-31      
Entity Well-known Seasoned Issuer Yes      
Entity Voluntary Filers No      
Entity Public Float     $ 313,633,817  
ICFR Auditor Attestation Flag true      
Document Financial Statement Error Correction [Flag] true      
Documents Incorporated by Reference
Portions of the Registrant’s Proxy Statement related to its annual meeting of stockholders are incorporated by reference in this Form 10-K in response to Part III Items 10, 11, 12, 13, and 14.