Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net income	$ 72,507	$ 50,613	$ 133,624	$ 102,018
Other comprehensive income
Unrealized (loss) gain on foreign currency remeasurement	(35,088)	20,045	(24,350)	27,815
Realized and unrealized gain (loss) on derivative financial instruments	24,855	(8,196)	21,920	(12,121)
Other comprehensive (loss) income	(10,233)	11,849	(2,430)	15,694
Comprehensive income	62,274	62,462	131,194	117,712
Comprehensive income attributable to non-controlling interests	(195)		(353)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 62,079	$ 62,462	$ 130,841	$ 117,712