Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 22, 2014
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2014
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q1
Trading Symbol	BXMT
Entity Registrant Name	BLACKSTONE MORTGAGE TRUST, INC.
Entity Central Index Key	0001061630
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		48,476,651