Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net income	$ 57,810	$ 66,392	$ 159,829	$ 193,040
Other comprehensive income
Unrealized gain (loss) on foreign currency remeasurement	16,175	(10,128)	43,990	(25,472)
Realized and unrealized (loss) gain on derivative financial instruments	(8,029)	5,882	(20,150)	11,841
Other comprehensive income (loss)	8,146	(4,246)	23,840	(13,631)
Comprehensive income	65,956	62,146	183,669	179,409
Comprehensive income attributable to non-controlling interests	(88)	(1,598)	(88)	(8,119)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 65,868	$ 60,548	$ 183,581	$ 171,290