v3.25.4
Cover Page - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2025
Feb. 04, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Document Transition Report false    
Entity File Number 1-14788    
Entity Registrant Name Blackstone Mortgage Trust, Inc.    
Entity Incorporation, State or Country Code MD    
Entity Tax Identification Number 94-6181186    
Entity Address, Address Line One 345 Park Avenue    
Entity Address, City or Town New York    
Entity Address, State or Province NY    
Entity Address, Postal Zip Code 10154    
City Area Code 212    
Local Phone Number 655-0220    
Title of 12(b) Security Class A common stock,    
Trading Symbol BXMT    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 3.2
Entity Common Stock, Shares Outstanding   168,738,642  
Documents Incorporated by Reference Part III of this annual report on Form 10-K incorporates information by reference from the registrant’s definitive proxy statement with respect to its 2026 annual
meeting of stockholders to be filed with the Securities and Exchange Commission within 120 days after the close of the registrant’s fiscal year.
    
Entity Central Index Key 0001061630    
Amendment Flag false    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Current Fiscal Year End Date --12-31