Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net income	$ 75,394	$ 78,293	$ 227,811	$ 211,917
Other comprehensive income
Unrealized loss on foreign currency translation	(39,961)	(2,416)	(44,125)	(26,766)
Realized and unrealized gain on derivative financial instruments	35,987	1,703	44,953	23,623
Other comprehensive (loss) income	(3,974)	(713)	828	(3,143)
Comprehensive income	71,420	77,580	228,639	208,774
Comprehensive income attributable to non-controlling interests	(497)	(128)	(1,176)	(481)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 70,923	$ 77,452	$ 227,463	$ 208,293