Cover Page - shares	3 Months Ended
	Mar. 31, 2024	Apr. 17, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-14788
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, Address Line Two	24th Floor
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		173,584,034
Entity Central Index Key	0001061630
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31