Mortgages Payable - Summary of Outstanding Mortgages Payable Narrative (Detail) - Mortgages - USD ($) $ in Thousands		9 Months Ended
	Oct. 03, 2018	Sep. 30, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Deferred debt issuance costs, accumulated amortization		$ 10,219	$ 6,315
Paramus
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Maturity date		Oct. 05, 2018
Retail Space | Rego Park I
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Percentage of cash mortgage collateralized		100.00%
Refinance date		May 11, 2018
Repayment date		Jun. 06, 2018
Retail Space | Rego Park II
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Maturity date		Nov. 30, 2018
Retail Space | 731 Lexington Avenue
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Maturity date		Aug. 01, 2022
Subsequent Event | Paramus
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Maturity date	Oct. 04, 2021