Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Significant Of Accounting Policies [Line Items]
Assets excluding BREIT OP	$ 2,700,000	$ 947,900
Liabilities excluding BREIT OP	1,900,000	645,500
Subscriptions received in advance, common stock	155,400	107,600
Investments in real estate-related securities	2,029,334	915,742
Undiscounted future minimum lease payments due	467,100
Level 2 [Member]
Significant Of Accounting Policies [Line Items]
Investments in real estate-related securities	2,000,000	$ 915,700
Level 3 [Member]
Significant Of Accounting Policies [Line Items]
Mortgage notes, term loans, and revolving credit facilities, repurchase agreements, and affiliate line of credit	$ 25,200