Area of a real estate property.

No definition available.

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Debt (Narratives) (Details)					1 Months Ended	3 Months Ended	12 Months Ended
Debt (Narratives) (Details)	Dec. 02, 2016 USD ($) ft²	Nov. 07, 2016 USD ($) Extensions CreditFacilities	Sep. 06, 2016 USD ($) ft²	Feb. 08, 2016 USD ($) ft²	Dec. 21, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2016	Mar. 15, 2016 USD ($)
Debt Instrument
Principal amount of mortgage loans							$ 9,278,263,000	$ 9,513,713,000
Net proceeds from borrowings							2,403,898,000	4,468,872,000	$ 2,428,285,000
Real estate impairment losses							161,165,000	256,000	26,518,000
Mortgages payable, net							9,278,263,000	9,513,713,000
Total assets							20,814,847,000	21,143,293,000	21,157,980,000
Liabilities							11,917,905,000	12,437,994,000
Gain (Loss) from disposal of real estate							$ 5,074,000	$ 65,396,000	$ 507,192,000
Secured Debt \| 770 Broadway \| Interest rate Swap
Debt Instrument
Debt Term				4 years 6 months
Secured Debt \| 770 Broadway \| Fixed Rate \| Interest rate Swap
Debt Instrument
Interest Rate, End of Period (in percentage)				2.56%
Secured Debt \| 770 Broadway \| Office
Debt Instrument
Interest Rate, End of Period (in percentage)							2.40%
Square Footage Of Real Estate Property \| ft²				1,158,000
Refinancing				$ 700,000,000
Net proceeds from borrowings				$ 330,000,000
Debt Term				5 years
Secured Debt \| 770 Broadway \| Office \| LIBOR
Debt Instrument
Debt Instrument, Description of Variable Rate Basis				LIBOR
Spread Over LIBOR (in percentage)				1.75%
Secured Debt \| 770 Broadway \| Office \| Previous First Mortgages
Debt Instrument
Interest Rate, End of Period (in percentage)				5.65%
Principal amount of mortgage loans				$ 353,000,000
Debt Instrument Maturity				March 2016
Secured Debt \| theMART
Debt Instrument
Square Footage Of Real Estate Property \| ft²			3,652,000
Refinancing			$ 675,000,000
Net proceeds from borrowings			$ 124,000,000
Debt Instrument Amortization Period			5 years
Secured Debt \| theMART \| Fixed Rate
Debt Instrument
Interest Rate, End of Period (in percentage)			2.70%
Secured Debt \| theMART \| Previous First Mortgages \| Fixed Rate
Debt Instrument
Interest Rate, End of Period (in percentage)			5.57%
Principal amount of mortgage loans			$ 550,000,000
Debt Instrument Maturity			December 2016
Secured Debt \| 350 Park Avenue
Debt Instrument
Square Footage Of Real Estate Property \| ft²	571,000
Refinancing	$ 400,000,000
Net proceeds from borrowings	$ 111,000,000
Debt Term	10 years
Secured Debt \| 350 Park Avenue \| Fixed Rate
Debt Instrument
Interest Rate, End of Period (in percentage)	3.92%
Secured Debt \| 350 Park Avenue \| Previous First Mortgages \| Fixed Rate
Debt Instrument
Interest Rate, End of Period (in percentage)	3.75%
Principal amount of mortgage loans	$ 284,000,000
Debt Instrument Maturity	January 2017
Secured Debt \| Skyline Properties
Debt Instrument
Principal amount of mortgage loans											$ 678,000,000
Real estate impairment losses						$ 160,700,000
Weighted average interest rate						2.97%				4.51%
Secured Debt \| Skyline Properties \| Discontinued Operations
Debt Instrument
Interest expense accrued							$ 7,823,000
Total assets					$ 236,535,000
Liabilities					724,412,000
Gain (Loss) from disposal of real estate					$ 487,877,000
Secured Debt \| Skyline Properties \| Discounted Cash Flow Valuation Technique
Debt Instrument
Discount rates						8.20%
Capitalization rate						8.00%
Unsecured Debt
Debt Instrument
Interest Rate, End of Period (in percentage)							1.88%
Unsecured Debt \| Revolving credit facility
Debt Instrument
Usecured credit facility, maximum borrowing capacity		$ 1,250,000,000
Number Of Revolving Credit Facilities \| CreditFacilities		1
Number Of Debt Instrument Available \| CreditFacilities		2
Debt Instrument Maturity		February 2021
Number Of Extensions Available \| Extensions		2
Length Of Extension Available		6 months
Facility Fee (in percentage)		0.20%
Unsecured Debt \| Revolving credit facility \| LIBOR
Debt Instrument
Debt Instrument, Description of Variable Rate Basis		LIBOR
Spread Over LIBOR (in percentage)		1.00%
Unsecured Debt \| Revolving credit facility \| Previous First Mortgages
Debt Instrument
Debt Instrument Maturity		June 2017
Unsecured Debt \| Revolving credit facility \| Previous First Mortgages \| LIBOR
Debt Instrument
Debt Instrument, Description of Variable Rate Basis		LIBOR
Spread Over LIBOR (in percentage)		1.15%