Investments in Real Estate Debt - Schedule of Company's Affiliate Investments In Real Estate Debt (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	$ 5,168,122		$ 5,168,122		$ 4,493,288
Commercial Mortgage Backed Securities Collateralized by Properties Owned by Blackstone-advised Investment Vehicles [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	1,485,509		1,485,509		1,418,056
Interest Income	14,197	$ 12,290	31,013	$ 24,370
Loans Collateralized by Properties Owned by Blackstone-advised Investment Vehicles [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	509,919		509,919		134,076
Interest Income	3,683		6,900
Commercial Mortgage Backed Securities Collateralized by Loans Originated by Blackstone-advised Investment Vehicle [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	132,640		132,640		155,978
Interest Income	1,369	2,090	2,957	4,187
Commercial Mortgage Backed Securities Collateralized by Properties and Loans Owned by Blackstone-advised Investment Vehicles [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	2,128,068		2,128,068		$ 1,708,110
Interest Income	$ 19,249	$ 14,380	$ 40,870	$ 28,557