Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Accumulated Deficit [Member]	Blackstone Mortgage Trust Inc [Member]	Non-Controlling Interests [Member]	Class A Common Stock [Member] Common Stock [Member]
Balance at Dec. 31, 2013	$ 756,750	$ 1,252,986	$ 798	$ (536,170)	$ 717,909	$ 38,841	$ 295
Shares of class A common stock issued, net	510,845	510,654			510,845		191
Restricted class A common stock earned	4,027	4,029			4,027		(2)
Dividends reinvested		97		(97)
Deferred directors' compensation	188	188			188
Other comprehensive income (loss)	1,930		1,930		1,930
Net income	51,555			46,531	46,531	5,024
Dividends declared on common stock	(42,122)			(42,122)	(42,122)
Distributions to non-controlling interests	(1,148)					(1,148)
Balance at Jun. 30, 2014	1,282,025	1,767,954	2,728	(531,858)	1,239,308	42,717	484
Balance at Dec. 31, 2014	1,500,886	2,027,404	(15,024)	(547,592)	1,465,371	35,515	583
Shares of class A common stock issued, net	1,029,557	1,029,208			1,029,557		349
Restricted class A common stock earned	6,504	6,504			6,504
Dividends reinvested	7	125		(118)	7
Deferred directors' compensation	188	188			188
Other comprehensive income (loss)	(4,308)		(4,308)		(4,308)
Net income	78,512			64,679	64,679	13,833
Dividends declared on common stock	(78,874)			(78,874)	(78,874)
Distributions to non-controlling interests	(36,985)					(36,985)
Balance at Jun. 30, 2015	$ 2,495,487	$ 3,063,429	$ (19,332)	$ (561,905)	$ 2,483,124	$ 12,363	$ 932