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

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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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

Amount, after accumulated amortization, of debt discount (premium).

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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

+ Details

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

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Debt - Schedule of Long term Debt (Details) - USD ($)	12 Months Ended
Debt - Schedule of Long term Debt (Details) - USD ($)	Dec. 31, 2018	Jan. 31, 2018	Dec. 31, 2017	Aug. 31, 2017	Aug. 31, 2014
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 0		$ 0
Deferred financing costs, net	(15,288,000)		(17,407,000)
Total	608,567,000		717,164,000
Fixed rate mortgage debt
Debt Instrument [Line Items]
Fixed rate debt	614,612,000		721,224,000
Total principal	1,929,612,000		1,701,224,000
Unamortized (discount) premiums, net of unamortized premiums (discount)	(1,647,000)		(3,370,000)
Deferred financing costs, net	(9,032,000)		(9,133,000)
Total	1,918,933,000		1,688,721,000
Fixed rate mortgage debt \| Metro Center
Debt Instrument [Line Items]
Fixed rate debt	$ 91,838,000		93,948,000
Stated Rate	3.59%
Effective rate (in percentage)	3.68%
Fixed rate mortgage debt \| 10 Union Square
Debt Instrument [Line Items]
Fixed rate debt	$ 50,000,000		50,000,000
Stated Rate	3.70%
Effective rate (in percentage)	3.97%
Fixed rate mortgage debt \| 1542 Third Avenue
Debt Instrument [Line Items]
Fixed rate debt	$ 30,000,000		30,000,000
Stated Rate	4.29%
Effective rate (in percentage)	4.53%
Fixed rate mortgage debt \| First Stamford Place
Debt Instrument [Line Items]
Fixed rate debt	$ 180,000,000		180,000,000
Stated Rate	4.28%
Effective rate (in percentage)	4.45%
Fixed rate mortgage debt \| First Stamford Place - First Lien
Debt Instrument [Line Items]
Stated Rate	4.09%
Face amount	$ 164,000,000
Fixed rate mortgage debt \| First Stamford Place - Second Lien
Debt Instrument [Line Items]
Stated Rate	6.25%
Face amount	$ 16,000,000
Fixed rate mortgage debt \| 1010 Third Avenue and 77 West 55th Street
Debt Instrument [Line Items]
Fixed rate debt	$ 38,995,000		39,710,000
Stated Rate	4.01%
Effective rate (in percentage)	4.22%
Fixed rate mortgage debt \| 10 Bank Street
Debt Instrument [Line Items]
Fixed rate debt	$ 33,779,000		34,602,000
Stated Rate	4.23%
Effective rate (in percentage)	4.35%
Fixed rate mortgage debt \| 383 Main Avenue
Debt Instrument [Line Items]
Fixed rate debt	$ 30,000,000		30,000,000
Stated Rate	4.44%
Effective rate (in percentage)	4.55%
Fixed rate mortgage debt \| 1333 Broadway
Debt Instrument [Line Items]
Fixed rate debt	$ 160,000,000	$ 66,600,000	66,602,000
Stated Rate	4.21%
Effective rate (in percentage)	4.29%
Face amount		$ 160,000,000.0
Fixed rate mortgage debt \| (first lien mortgage loan)
Debt Instrument [Line Items]
Fixed rate debt	$ 0		66,632,000
Stated Rate	0.00%
Effective rate (in percentage)	0.00%
Fixed rate mortgage debt \| (second lien mortgage loan)
Debt Instrument [Line Items]
Fixed rate debt	$ 0		9,172,000
Stated Rate	0.00%
Effective rate (in percentage)	0.00%
Fixed rate mortgage debt \| (first lien mortgage loan)
Debt Instrument [Line Items]
Fixed rate debt	$ 0		74,045,000
Stated Rate	0.00%
Effective rate (in percentage)	0.00%
Fixed rate mortgage debt \| (second lien mortgage loan)
Debt Instrument [Line Items]
Fixed rate debt	$ 0		9,369,000
Stated Rate	0.00%
Effective rate (in percentage)	0.00%
Fixed rate mortgage debt \| 1350 Broadway
Debt Instrument [Line Items]
Fixed rate debt	$ 0		37,144,000
Stated Rate	0.00%
Effective rate (in percentage)	0.00%
Senior unsecured notes - exchangeable \| Senior unsecured notes - exchangeable
Debt Instrument [Line Items]
Fixed rate debt	$ 250,000,000		250,000,000
Stated Rate	2.625%				2.625%
Effective rate (in percentage)	3.93%				3.80%
Face amount					$ 250,000,000
Senior unsecured notes - Series A, B, C, D, E and F \| Series A
Debt Instrument [Line Items]
Total	$ 100,000,000		100,000,000
Stated Rate	3.93%
Effective rate (in percentage)	3.96%
Senior unsecured notes - Series A, B, C, D, E and F \| Series B
Debt Instrument [Line Items]
Total	$ 125,000,000		125,000,000
Stated Rate	4.09%
Effective rate (in percentage)	4.12%
Senior unsecured notes - Series A, B, C, D, E and F \| Series C
Debt Instrument [Line Items]
Total	$ 125,000,000		125,000,000
Stated Rate	4.18%
Effective rate (in percentage)	4.21%
Senior unsecured notes - Series A, B, C, D, E and F \| Series D
Debt Instrument [Line Items]
Total	$ 115,000,000		$ 115,000,000
Stated Rate	4.08%		4.08%
Effective rate (in percentage)	4.11%
Face amount			$ 115,000,000.0
Senior unsecured notes - Series A, B, C, D, E and F \| Series E
Debt Instrument [Line Items]
Total	$ 160,000,000		$ 0
Stated Rate	4.26%		4.26%
Effective rate (in percentage)	4.27%
Face amount			$ 160,000,000.0
Senior unsecured notes - Series A, B, C, D, E and F \| Series F
Debt Instrument [Line Items]
Total	$ 175,000,000		$ 0
Stated Rate	4.44%		4.44%
Effective rate (in percentage)	4.45%
Face amount			$ 175,000,000.0
Revolving Credit Facility \| Unsecured revolving credit facility
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 0		0
Effective rate (in percentage)	3.60%
Revolving Credit Facility \| Unsecured revolving credit facility \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.10%
Revolving Credit Facility \| Unsecured term loan facility
Debt Instrument [Line Items]
Unsecured revolving credit facility	$ 265,000,000		$ 265,000,000	$ 265,000,000
Effective rate (in percentage)	2.1485%
Pay rate	3.35%
Revolving Credit Facility \| Unsecured term loan facility \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.20%