Notes Receivable, Net - Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Accounts Notes And Loans Receivable [Line Items]
Increase in allowance for credit loss		$ 500
Notes receivable		$ 159,638	$ 102,100
OP Units in settlement of note receivable		21,109
Settlement amount of note receivable in OP units		$ 500
Note receivable accrued interest		19,208	13,917
Notes Receivable		158,468	101,450
Credit loss reserve		1,170	650
Notes receivable, net		$ 158,468	101,450
Interest Rate		9.00%
Additional credit loss reserve			300
Aggregate loans		$ 158,468	101,450
LUF Portfolio
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest			$ 5,000
Interest Rate			8.00%
Percentage of mortgage loan collateralized			5000.00%
Core Note
Accounts Notes And Loans Receivable [Line Items]
Notes receivable modified, subsequent payment default		21,600	$ 21,600
850 Third Avenue Brooklyn, NY
Accounts Notes And Loans Receivable [Line Items]
Notes Receivable			54,000
Notes receivable, net			$ 54,000
Interest Rate			9.00%
Fund II
Accounts Notes And Loans Receivable [Line Items]
Notes receivable			$ 33,800
Note receivable accrued interest			600
Notes Receivable			33,800
Notes receivable, net			33,800
Fund III
Accounts Notes And Loans Receivable [Line Items]
Notes receivable modified, subsequent payment default		$ 10,000
ASU 2016-13
Accounts Notes And Loans Receivable [Line Items]
Credit loss reserve			400
Maximum
Accounts Notes And Loans Receivable [Line Items]
Interest Rate		12.00%
Minimum
Accounts Notes And Loans Receivable [Line Items]
Interest Rate		5.00%
Core Portfolio
Accounts Notes And Loans Receivable [Line Items]
Notes receivable	[1]	$ 154,332	96,794
Core Portfolio | Silver Spring, Maryland
Accounts Notes And Loans Receivable [Line Items]
Notes Receivable		16,000
Notes receivable, net		16,000
Core Portfolio | Soho, New York
Accounts Notes And Loans Receivable [Line Items]
Notes Receivable		43,000
Notes receivable, net		$ 43,000
Core Portfolio | Maximum
Accounts Notes And Loans Receivable [Line Items]
Interest Rate	[1]	12.00%
Core Portfolio | Minimum
Accounts Notes And Loans Receivable [Line Items]
Interest Rate	[1]	5.00%
Core Portfolio | Three Tranches
Accounts Notes And Loans Receivable [Line Items]
Notes Receivable		$ 42,000
Notes receivable, net		42,000
Structured Financing
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest		8,800
Aggregate loans		37,900
Structured Financing | Non-Collateral Dependent Loans
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest		10,400
Credit loss reserve		1,200
Loans amortized cost		$ 140,900
Brandywine Portfolio | Core Portfolio
Accounts Notes And Loans Receivable [Line Items]
Notes receivable			38,700
Note receivable accrued interest			$ 2,000
Equity method investment, ownership percentage by third party			24.78%

[1] Includes one and two notes receivable from OP Unit holders, with balances totaling $6.0 million and $6.5 million at September 30, 2021 and December 31, 2020, respectively