Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net income	$ 75,551	$ 72,507	$ 152,418	$ 133,624
Other comprehensive income
Unrealized loss on foreign currency translation	(9,578)	(35,088)	(4,164)	(24,350)
Realized and unrealized gain on derivative financial instruments	10,914	24,855	8,966	21,920
Other comprehensive income (loss)	1,336	(10,233)	4,802	(2,430)
Comprehensive income	76,887	62,274	157,220	131,194
Comprehensive income attributable to non-controlling interests	(377)	(195)	(680)	(353)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 76,510	$ 62,079	$ 156,540	$ 130,841