Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Net income	$ 84,404	$ 90,769	$ 297,412	$ 55,991
Other comprehensive income
Unrealized (loss) gain on foreign currency translation	(46,952)	62,656	(66,356)	14,488
Realized and unrealized gain (loss) on derivative financial instruments	46,083	(61,936)	65,059	11,390
Other comprehensive (loss) income	(869)	720	(1,297)	25,878
Comprehensive income	83,535	91,489	296,115	81,869
Comprehensive income attributable to non-controlling interests	(647)	(909)	(2,158)	(1,937)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 82,888	$ 90,580	$ 293,957	$ 79,932