Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Net income	$ 10,526	$ 12,900	$ 15,696	$ 156,873
Other comprehensive income
Unrealized gain on derivative financial instruments		2,103		5,852
Gain on interest rate swaps no longer designated as cash flow hedges				2,481
Amortization of unrealized gains and losses on securities		(4)		(769)
Amortization of deferred gains and losses on settlement of swaps				(56)
Other-than-temporary impairments of securities related to fair value adjustments in excess of expected credit losses, net of amortization		206		419
Other comprehensive income		2,305		7,927
Comprehensive income	10,526	15,205	15,696	164,800
Less: Comprehensive income attributable to non-controlling interests	(2,206)	(5,901)	(7,743)	(81,048)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 8,320	$ 9,304	$ 7,953	$ 83,752