Investments in Real Estate Debt - Schedule of Company's Affiliate Investments In Real Estate Debt (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	$ 5,297,531		$ 5,297,531		$ 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	1,725,919		1,725,919		1,418,056
Interest Income	13,799	$ 13,580	44,812	$ 37,950
Loans Collateralized by Properties Owned by Blackstone-advised Investment Vehicles [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Cost Basis	528,298		528,298		134,076
Interest Income	5,968		12,868
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	128,043		128,043		155,978
Interest Income	1,089	2,012	4,046	6,199
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	2,382,260		2,382,260		$ 1,708,110
Interest Income	$ 20,856	$ 15,592	$ 61,726	$ 44,149