Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net income	$ 78,293	$ 57,810	$ 211,917	$ 159,829
Other comprehensive income
Unrealized (loss) gain on foreign currency remeasurement	(2,416)	16,175	(26,766)	43,990
Realized and unrealized gain (loss) on derivative financial instruments	1,703	(8,029)	23,623	(20,150)
Other comprehensive (loss) income	(713)	8,146	(3,143)	23,840
Comprehensive income	77,580	65,956	208,774	183,669
Comprehensive income attributable to non-controlling interests	(128)	(88)	(481)	(88)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 77,452	$ 65,868	$ 208,293	$ 183,581