Document and Entity Information	3 Months Ended
	Mar. 31, 2013	May 06, 2013
Document And Entity Information
Entity Registrant Name	BLACKSTONE MORTGAGE TRUST, INC.
Entity Central Index Key	0001061630
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Is Entity's Reporting Status Current?	Yes
Well-known seasoned issuer?	No
Entity Voluntary Filers?	No
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		2,926,651
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2013