Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net income	$ 285,813	$ 217,968	$ 246,440
Other comprehensive income
Unrealized (loss) gain on foreign currency translation	(44,317)	47,124	(49,686)
Realized and unrealized gain (loss) on derivative financial instruments	39,801	(20,628)	26,242
Other comprehensive (loss) income	(4,516)	26,496	(23,444)
Comprehensive income	281,297	244,464	222,996
Comprehensive income attributable to non-controlling interests	(735)	(337)	(8,143)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 280,562	$ 244,127	$ 214,853