Notes payable gross.

No definition available.

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- Definition

Percentage of cash mortgage collateralized

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Amount of accumulated amortization of debt issuance 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

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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- Details

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Data Type:	na
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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Mortgages Payable (Outstanding mortgages payable) (Details) - USD ($) $ in Thousands		5 Months Ended	12 Months Ended
	Jun. 01, 2017	May 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate
Percentage of cash mortgage collateralized			100.00%
Deferred debt issuance costs, net of accumulated amortization of $6,315 and $6,824, respectively			$ (12,218)
Notes Payable (in US dollars)			1,240,222	$ 1,052,359
Mortgages \| 731 Lexington Avenue \| Office space
Mortgage Loans on Real Estate
Maturity date	Jun. 01, 2020
Notes Payable (in US dollars)	$ 500,000	$ 300,000
Mortgages \| 731 Lexington Avenue \| Office space \| LIBOR
Mortgage Loans on Real Estate
Basis spread over LIBOR	0.90%	0.95%
Mortgages \| Secured loan
Mortgage Loans on Real Estate
Notes payable, gross			1,252,440	1,056,147
Deferred debt issuance costs, net of accumulated amortization of $6,315 and $6,824, respectively			(12,218)	(3,788)
Notes Payable (in US dollars)			1,240,222	1,052,359
Deferred debt issuance costs, accumulated amortization			$ 6,315	$ 6,824
Mortgages \| Secured loan \| Rego Park I
Mortgage Loans on Real Estate
Maturity date			Mar. 10, 2018
Interest rate			0.35%
Percentage of cash mortgage collateralized			100.00%	100.00%
Notes payable, gross			$ 78,246	$ 78,246
Mortgages \| Secured loan \| Paramus
Mortgage Loans on Real Estate
Maturity date			Oct. 05, 2018
Interest rate			2.90%
Notes payable, gross			$ 68,000	68,000
Mortgages \| Secured loan \| Rego Park II
Mortgage Loans on Real Estate
Maturity date			Nov. 30, 2018
Interest rate			3.42%
Notes payable, gross			$ 256,194	259,901
Mortgages \| Secured loan \| Rego Park II \| LIBOR
Mortgage Loans on Real Estate
Basis spread over LIBOR			1.85%
Mortgages \| Secured loan \| 731 Lexington Avenue \| Retail space
Mortgage Loans on Real Estate
Maturity date			Aug. 05, 2022
Interest rate			2.78%
Notes payable, gross			$ 350,000	350,000
Mortgages \| Secured loan \| 731 Lexington Avenue \| Retail space \| LIBOR
Mortgage Loans on Real Estate
Basis spread over LIBOR			1.40%
Mortgages \| Secured loan \| 731 Lexington Avenue \| Office space
Mortgage Loans on Real Estate
Maturity date			Jun. 11, 2024
Interest rate			2.38%
Notes payable, gross			$ 500,000	$ 300,000
Mortgages \| Secured loan \| 731 Lexington Avenue \| Office space \| LIBOR
Mortgage Loans on Real Estate
Basis spread over LIBOR			0.90%