Mortgages Payable - Summary of Outstanding Mortgages Payable (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Mortgage Loans on Real Estate [Line Items]
Notes payable	$ 1,162,632	$ 1,240,222
Mortgages
Mortgage Loans on Real Estate [Line Items]
Mortgage payable gross	1,172,234	1,252,440
Deferred debt issuance costs, net of accumulated amortization of $8,915 and $6,315, respectively	(9,602)	(12,218)
Notes payable	$ 1,162,632	1,240,222
Mortgages \| Paramus
Mortgage Loans on Real Estate [Line Items]
Maturity date	Oct. 05, 2018
Interest rate (in percentage)	2.90%
Mortgage payable gross	$ 68,000	68,000
Mortgages \| Rego Park II \| Retail Space
Mortgage Loans on Real Estate [Line Items]
Maturity date	Nov. 30, 2018
Interest rate (in percentage)	3.94%
Mortgage payable gross	$ 254,234	256,194
Mortgages \| 731 Lexington Avenue \| Retail Space
Mortgage Loans on Real Estate [Line Items]
Maturity date	Aug. 01, 2022
Interest rate (in percentage)	3.41%
Mortgage payable gross	$ 350,000	350,000
Mortgages \| 731 Lexington Avenue \| Office Space
Mortgage Loans on Real Estate [Line Items]
Maturity date	Jun. 01, 2024
Interest rate (in percentage)	2.97%
Mortgage payable gross	$ 500,000	500,000
Mortgages \| Rego Park I \| Retail Space
Mortgage Loans on Real Estate [Line Items]
Interest rate (in percentage)	0.00%
Mortgage payable gross	$ 0	$ 78,246

Notes payable gross.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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