Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net income (loss)	$ 132,468	$ 18,505	$ 213,008	$ (34,780)
Other comprehensive income
Unrealized gain (loss) on foreign currency translation	15,553	21,342	(19,404)	(48,166)
Realized and unrealized (loss) gain on derivative financial instruments	(16,094)	(30,665)	18,977	73,325
Other comprehensive (loss) income	(541)	(9,323)	(427)	25,159
Comprehensive income (loss)	131,927	9,182	212,581	(9,621)
Comprehensive income attributable to non-controlling interests	(873)	(961)	(1,511)	(1,028)
Comprehensive income (loss) attributable to Blackstone Mortgage Trust, Inc.	$ 131,054	$ 8,221	$ 211,070	$ (10,649)