Notes Receivable, Net - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Apr. 01, 2020	Mar. 28, 2018	Nov. 16, 2017	May 01, 2017
Accounts Notes And Loans Receivable [Line Items]
Notes receivable	$ 135,562,000	$ 114,943,000
Note receivable accrued interest	10,680,000	9,872,000
Notes receivable, net	134,692,000	114,943,000
Additional credit loss reserve	500,000
Credit loss reserves	870,000
Credit loss reserves	134,692,000	114,943,000
Core Portfolio
Accounts Notes And Loans Receivable [Line Items]
Notes receivable	96,794,000	$ 76,467,000
Equity method investment, ownership percentage by third party		24.78%		14.11%	38.89%
Notes receivable modified, subsequent payment default		$ 20,800
Proceeds from notes receivable		4,300,000
Notes receivable defer interest until maturity		400,000
Structured Financing
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest	3,500,000
Loans amortized cost	0
Credit loss reserves	54,800,000
Structured Financing | Non-Collateral Dependent Loans
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest	7,200,000
Loans amortized cost	91,500,000
Credit loss reserves	900,000
Brandywine Portfolio | Core Portfolio
Accounts Notes And Loans Receivable [Line Items]
Notes receivable	38,700,000	38,700,000
Note receivable accrued interest	$ 2,000,000.0
Equity method investment, ownership percentage by third party	24.78%		24.78%
Notes receivable, net						$ 153,400,000
ASU 2016-13
Accounts Notes And Loans Receivable [Line Items]
Credit loss reserve	$ 400,000
LUF Portfolio
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest	$ 5,000,000.0
Interest Rate	8.00%
Percentage of mortgage loan collateralized	50.00%
Core Note
Accounts Notes And Loans Receivable [Line Items]
Notes receivable modified, subsequent payment default	$ 21,300,000	$ 21,300,000
850 Third Avenue Brooklyn, NY
Accounts Notes And Loans Receivable [Line Items]
Notes receivable, net	$ 54,000,000.0
Interest Rate	9.00%
Pacesetter Park
Accounts Notes And Loans Receivable [Line Items]
Interest Rate		5.10%
Note receivable exchanged for sale of real estate		$ 13,500,000
Fund II
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest	$ 300,000	400,000
Fund III
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest		4,700,000
Notes receivable modified, subsequent payment default	$ 10,000,000.0
Fund IV
Accounts Notes And Loans Receivable [Line Items]
Proceeds from notes receivable		15,300,000
Note receivable accrued interest		$ 10,000,000.0