Mortgages Payable - Additional Information (Detail)	1 Months Ended	5 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($)	May 31, 2017 USD ($)	Jun. 30, 2017 USD ($) Option	Dec. 31, 2016 USD ($)
Mortgage Loans on Real Estate [Line Items]
Notes Payable	$ 1,239,729,000		$ 1,239,729,000	$ 1,052,359,000
Mortgages [Member]
Mortgage Loans on Real Estate [Line Items]
Notes Payable	1,239,729,000		1,239,729,000	$ 1,052,359,000
731 Lexington Avenue [Member] \| Office Space [Member] \| Mortgages [Member]
Mortgage Loans on Real Estate [Line Items]
Notes Payable	$ 500,000,000	$ 300,000,000	$ 500,000,000
Debt Instrument, Description of Variable Rate Basis		LIBOR	LIBOR
Debt instrument maturity date	Jun. 11, 2024	Mar. 11, 2021	Jun. 11, 2024
Derivative Liability Notional Amount	$ 500,000,000		$ 500,000,000
Number of one-year extension options \| Option			4
731 Lexington Avenue [Member] \| Office Space [Member] \| Mortgages [Member] \| LIBOR [Member]
Mortgage Loans on Real Estate [Line Items]
Basis spread over LIBOR	0.90%	0.95%	0.90%
Derivative cap interest rate, LIBOR	6.00%		6.00%

Number of one-year extension options.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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- Definition

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

+ References

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- Definition

Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

+ References

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- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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- Definition

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

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-Name Accounting Standards Codification
-Topic 944
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-Section S99
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-Publisher FASB
-Name Accounting Standards Codification
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