Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 15, 2016	Jun. 15, 2016	May 09, 2014	May 31, 2013	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Mar. 25, 2014
Class of Stock [Line Items]
Total stock, shares authorized					300,000,000		300,000,000
Preferred stock, shares authorized					100,000,000		100,000,000
Preferred stock issued					0		0
Preferred stock outstanding					0		0
Plan adoption date					Mar. 25, 2014
Dividends declared per share of common stock		$ 0.62			$ 0.62	$ 0.52	$ 1.24	$ 1.04
Date of dividend paid							Jul. 15, 2016
Date of dividend declared							Jun. 15, 2016
Record date of dividend paid							Jun. 30, 2016
Accumulated other comprehensive loss					$ 42,143		$ 42,143		$ 32,758
Unrealized gain related to changes in fair value of derivative instruments					31,000		31,000		25,000
Cumulative unrealized currency translation adjustment on assets and liabilities denominated in foreign currencies					73,100		73,100		57,800
CT Legacy Partners' total equity					21,700		21,700		22,500
Equity interests owned by Blackstone Mortgage Trust, Inc.					9,000		9,000		9,400
Non-controlling interests in CT Legacy Partners					$ 12,700		$ 12,700		$ 13,100
Subsequent Events [Member]
Class of Stock [Line Items]
Dividends paid	$ 58,200
Dividends paid per common stock	$ 0.62
Class A Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized					200,000,000		200,000,000		200,000,000
Common stock, shares issued under dividend reinvestment component					265	134	550	273
Number of shares sold during period				25,875,000			550	34,780,298
Class A Common Stock [Member] | ATM Agreements [Member]
Class of Stock [Line Items]
Aggregate sales price			$ 200,000
Number of shares sold during period							0	0
Aggregate sales price remaining available					$ 188,600		$ 188,600
Dividend Reinvestment and Direct Stock Purchase Plan [Member] | Class A Common Stock [Member]
Class of Stock [Line Items]
Reserved for issuance of class A common stock					9,998,847		9,998,847			10,000,000