Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Mortgages payable, net of deferred debt issuance costs	$ (970,961)	$ (965,826)
Right-of-use asset	4,529
Lease liability	4,845
Real estate, net	$ 716,843	730,270
Cash and cash equivalent maturity maximum	3 months
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use asset				$ 5,058
Lease liability				$ 5,428
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Loan participation balance		195,708
Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Property rentals		152,795	$ 152,857
Expense reimbursements		80,030	$ 77,717
Restatement To Reclassify Rego Park II As A Reduction To Mortage Payable, Net Of Deferred Debt Issuance Costs | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Mortgages payable, net of deferred debt issuance costs		$ 195,708