Consolidated Statements of Changes in Equity (USD $) In Thousands	Total	Class A Common Stock [Member]	Restricted Class A Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Accumulated Deficit [Member]	Blackstone Mortgage Trust Inc [Member]	Non-Controlling Interests [Member]
Balance at Dec. 31, 2012	$ 153,453	$ 293		$ 609,002		$ (535,851)	$ 73,444	$ 80,009
Reverse stock split		(263)		263
Shares of class A common stock issued	633,810	258		633,552			633,810
Deferred directors' compensation	169			169			169
Net income	15,696					7,953	7,953	7,743
Consolidation of subsidiary	11,962					5,727	5,727	6,235
Contributions from non-controlling interests	15,000							15,000
Dividends declared on common stock	(7,776)					(7,776)	(7,776)
Purchase of and distributions to non-controlling interests	(18,772)							(18,772)
Balance at Sep. 30, 2013	803,542	288		1,242,986		(529,947)	713,327	90,215
Balance at Dec. 31, 2013	756,750	288	7	1,252,986	798	(536,170)	717,909	38,841
Shares of class A common stock issued	763,407	284		763,123			763,407
Restricted class A common stock earned	5,552		(2)	5,554			5,552
Dividends reinvested				149		(149)
Deferred directors' compensation	281			281			281
Other comprehensive loss	(7,003)				(7,003)		(7,003)
Net income	75,157					68,555	68,555	6,602
Dividends declared on common stock	(70,962)					(70,962)	(70,962)
Distributions to non-controlling interests	(13,323)							(13,323)
Balance at Sep. 30, 2014	$ 1,509,859	$ 572	$ 5	$ 2,022,093	$ (6,205)	$ (538,726)	$ 1,477,739	$ 32,120