v3.26.1
Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2026
May 05, 2026
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Trading Symbol TSLX  
Entity Registrant Name Sixth Street Specialty Lending, Inc.  
Entity Central Index Key 0001508655  
Current Fiscal Year End Date --12-31  
Document Quarterly Report true  
Document Transition Report false  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity File Number 001-36364  
Entity Tax Identification Number 27-3380000  
Entity Incorporation, State or Country Code DE  
Entity Address, Address Line One 2100 McKinney Avenue  
Entity Address, Address Line Two Suite 1500  
Entity Address, City or Town Dallas  
Entity Address, State or Province TX  
Entity Address, Postal Zip Code 75201  
City Area Code 469  
Local Phone Number 621-3001  
Entity Common Stock, Shares Outstanding   95,019,600
Title of 12(b) Security Common Stock, par value $0.01 per share  
Security Exchange Name NYSE