Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Significant Of Accounting Policies [Line Items]
Assets excluding BREIT OP	$ 4,700,000,000	$ 4,700,000,000		$ 2,800,000,000
Liabilities excluding BREIT OP	3,300,000,000	3,300,000,000		1,900,000,000
Operating lease, ROU assets	110,764,000	110,764,000
Operating lease, liabilities	79,271,000	79,271,000
Account Standards Update 2016-02
Significant Of Accounting Policies [Line Items]
Ground leases discount rate			7.00%
Operating lease, ROU assets			$ 31,300,000
Operating lease, liabilities			31,300,000
Prepaid ground lease intangible asset reclassified as ROU operating asset			15,700,000
Below-market ground lease intangible asset reclassified as ROU operating asset	4,500,000	4,500,000
Above-market ground lease intangible liability reclassified as ROU operating asset	4,600,000	4,600,000
Straight-line ground rent liability reclassified as ROU operating asset	1,200,000	$ 1,200,000
Lease, practical expedients package		true
Lease, practical expedient, use of hindsight		false
Impact to retained earnings as a result of ASU adoption			$ 0
Rental revenue previously classified as tenant reimbursement income	18,300,000	$ 42,900,000
Level 2 [Member]
Significant Of Accounting Policies [Line Items]
Investments in real estate-related securities	3,800,000,000	3,800,000,000		$ 2,300,000,000
Level 3 [Member]
Significant Of Accounting Policies [Line Items]
Mortgage notes, term loans, secured and unsecured revolving credit facilities, repurchase agreements, and affiliate line of credit	$ 71,800,000	$ 71,800,000