Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net income	$ 307,393	$ 285,813	$ 217,968
Other comprehensive income
Unrealized gain (loss) on foreign currency translation	23,920	(44,317)	47,124
Realized and unrealized (loss) gain on derivative financial instruments	(5,931)	39,801	(20,628)
Other comprehensive income (loss)	17,989	(4,516)	26,496
Comprehensive income	325,382	281,297	244,464
Comprehensive income attributable to non-controlling interests	(1,826)	(735)	(337)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 323,556	$ 280,562	$ 244,127