Stockholders' Equity - Schedule of Basic and Diluted Earnings Per Share, Continuing Operations (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement [Abstract]
Income from continuing operations	$ 6,768	$ 3,692	$ 5,170	$ 144,887
Net income attributable to non-controlling interests	(4,020)	(1,068)	(5,537)	(75,137)
Income (loss) from continuing operations attributable to Blackstone Mortgage Trust, Inc.	$ 2,748	$ 2,624	$ (367)	$ 69,750
Weighted average shares outstanding	12,401,274	2,289,352	7,734,774	2,286,582
Warrants and options outstanding for the purchase of class A common stock		153,334		148,757
Weighted average shares outstanding, diluted	12,401,274	2,442,686	7,734,774	2,435,339
Per share amount, basic	$ 0.22	$ 1.15	$ (0.05)	$ 30.50
Per share amount, diluted	$ 0.22	$ 1.08	$ (0.05)	$ 28.65