Notes Receivable, Net - Additional Information (Details) - USD ($)		12 Months Ended
	Feb. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 02, 2020	Nov. 01, 2020	Apr. 01, 2020	Jan. 14, 2020	Mar. 28, 2018	Dec. 31, 2017	Nov. 16, 2017
Accounts Notes And Loans Receivable [Line Items]
Notes receivable		$ 102,100,000	$ 114,943,000
Note receivable accrued interest		13,917,000	9,872,000
Credit loss reserve		650,000
Notes receivable, net		101,450,000	114,943,000	$ 111,775,000						$ 160,991,000
Additional credit loss reserve		300,000
Proceeds from notes receivable			15,250,000	26,000,000
Credit loss reserves		101,450,000	114,943,000
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		21,600,000	$ 21,600,000
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]
Notes receivable					$ 33,800,000
Note receivable accrued interest			400,000			$ 600,000
Notes receivable, net		33,800,000
Fund III
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest			4,700,000	$ 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
ASU 2016-13
Accounts Notes And Loans Receivable [Line Items]
Credit loss reserve		400,000
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									14.11%		38.89%
Notes receivable modified, subsequent payment default			20,800,000
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		8,700,000
Loans amortized cost		0
Credit loss reserves		38,300,000
Structured Financing | Non-Collateral Dependent Loans
Accounts Notes And Loans Receivable [Line Items]
Note receivable accrued interest		5,200,000
Credit loss reserve		700,000
Loans amortized cost		$ 77,700,000
Brandywine Portfolio | Core Portfolio
Accounts Notes And Loans Receivable [Line Items]
Notes receivable							$ 38,700,000
Note receivable accrued interest							$ 2,000,000.0
Equity method investment, ownership percentage by third party							24.78%