Real Estate Real Estate Values (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Land	$ 4,609,337	$ 4,367,816
Property, Plant and Equipment, Gross [Abstract]
Investment Building and Building Improvements	14,580,915	14,262,616
Fixtures and Equipment, Gross	1,362,224	1,292,124
Projects under development	194,254	160,190
Land held for development	404,846	325,200
Investment in real estate	21,151,576	20,407,946
Real Estate Investment Property, Accumulated Depreciation	(4,880,808)	(4,539,583)
Investment in real estate, net	16,270,768	15,868,363
Projects under development [Member]
Property, Plant and Equipment, Gross [Abstract]
Land Under Development	76,250	75,646
Projects under development	118,004	84,544
Land held for development [Member]
Property, Plant and Equipment, Gross [Abstract]
Projects under development	54,744	26,104
Land held for development	$ 350,102	$ 299,096

Carrying amount of land for a real estate project that has not yet been completed.

No definition available.

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- Definition

The current amount of expenditures for a real estate project that has not yet been completed.

+ References

+ Details

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- Definition

Gross amount of fixtures and equipment as of the date of the statement of financial position. Fixtures may include and consist of: machinery, equipment, engines, boilers, incinerators, installed building materials; systems and equipment for the purpose of supplying or distributing heating, cooling, electricity, gas, water, air, or light; antennas, cable, wiring and conduits used in connection with radio, television, security, fire prevention, or fire detection or otherwise used to carry electronic signals; telephone systems and equipment; elevators and related machinery and equipment; fire detection, prevention and extinguishing systems and apparatus; security and access control systems and apparatus; plumbing systems; water heaters, ranges, stoves, microwave ovens, refrigerators, dishwashers, garbage disposers, washers, dryers and other appliances; light fixtures, awnings, storm windows and storm doors; pictures, screens, blinds, shades, curtains and curtain rods; mirrors; cabinets, paneling, rugs and floor and wall coverings; fences, trees and plants; swimming pools; and such other items as defined by the reporting entity.

+ References

No definition available.

+ Details

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- Definition

Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements.

+ References

+ Details

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- Definition

Carrying amount as of the balance sheet date of real estate held for productive use. This excludes land held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 4

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6812-107765

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 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Period Type:	instant

- Definition

Carrying amount of land available for development.

+ References

Reference 1: 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),1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph d

-Article 7

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(3))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 7

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- Definition

Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

+ Details

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- Definition

Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

+ Details

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