Equity - Schedule of Basic and Diluted Earnings Per Share, Continuing Operations (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share [Abstract]
Income from continuing operations	$ 25,424	$ 282,213	$ 253,209
Net income attributable to non-controlling interests	(10,392)	(98,780)	5,823
Income from continuing operations attributable to Blackstone Mortgage Trust, Inc.	$ 15,032	$ 183,433	$ 259,032
Weighted-average shares outstanding	18,520,052	2,345,943	2,266,043
Warrants and options outstanding for the purchase of class A common stock		129,351	129,000
Weighted-average shares outstanding, diluted	18,520,052	2,475,294	2,395,043
Per share amount, basic	$ 0.81	$ 78.19	$ 114.31
Per share amount, diluted	$ 0.81	$ 74.16	$ 108.17