Basis of Presentation - Additional Information (Detail) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Mortgages payable, net of deferred debt issuance costs		$ (969,673)		$ (965,826)
Number of reportable segments | segment		1
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Loan participation balance				195,708
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Property rentals	$ 38,250		$ 115,109
Expense reimbursements	$ 20,875		$ 60,149
Restatement to reclassify Rego Park II as a reduction to mortgage payable, net of deferred debt issuance costs | Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Mortgages payable, net of deferred debt issuance costs				$ 195,708