Mortgages Payable - Summary of Outstanding Mortgages Payable Narrative (Detail) - Mortgages - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Mortgage Loans on Real Estate [Line Items]
Deferred debt issuance costs, accumulated amortization	$ 7,628	$ 6,315
Retail Space \| Rego Park I
Mortgage Loans on Real Estate [Line Items]
Percentage of cash mortgage collateralized	100.00%
Mortgage loan extension date	2018-03

Amount of accumulated amortization of debt issuance costs.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_AccumulatedAmortizationDeferredFinanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant