Consolidated Statements of Changes in (Deficit) Equity (Unaudited) (USD $) In Thousands	Total	Class A Common Stock [Member]	Restricted Class A Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]	Total Blackstone Mortgage Trust, Inc. Stockholders' (Deficit) Equity [Member]	Non-controlling Interests [Member]
Balance, beginning at Dec. 31, 2011	$ (128,939)	$ 220	$ 2	$ 597,049	$ (40,584)	$ (667,111)	$ (110,424)	$ (18,515)
Net income	156,873					75,835	75,835	81,038
Other comprehensive income	7,927				7,917		7,917	10
Deconsolidation of CT Legacy Asset	1,293				1,293		1,293
Purchase of and distributions to non-controlling interests	(8)							(8)
Restricted class A common stock earned, net of shares deferred	651		3	648			651
Deferred directors' compensation	169			169			169
Balance, ending at Sep. 30, 2012	37,966	220	5	597,866	(31,374)	(591,276)	(24,559)	62,525
Balance, beginning at Dec. 31, 2012	153,453	293		609,002		(535,851)	73,444	80,009
Net income	15,696					7,953	7,953	7,743
Consolidation of subsidiary	11,962					5,727	5,727	6,235
Other comprehensive income
Contributions from non-controlling interests	15,000							15,000
Purchase of and distributions to non-controlling interests	(18,772)							(18,772)
Proceeds from offering of common stock	633,810	258		633,552			633,810
Reverse stock split		(263)		263
Dividends declared	(7,776)					(7,776)	(7,776)
Deferred directors' compensation	169			169			169
Balance, ending at Sep. 30, 2013	$ 803,542	$ 288		$ 1,242,986		$ (529,947)	$ 713,327	$ 90,215