Share Incentive Plans (Details Textuals) (USD $)	12 Months Ended
Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Share Incentive Plans (Textuals) [Abstract]
Maximum aggregate number of awards under Share Incentive Plan as a percentage of outstanding Common Shares	7.50%
Maximum aggregate number of awards under Share Incentive Plan	22,785,696
Shares available for future issuance	5,395,739
Number of installments for vesting of stock option	3
Restriction period of restricted shares	3 Years
Conversion of OP Units	one-for-one basis
Maximum no of years for attaining target under LTIP Units Award	Ten years following the date of issuance
Retirement age for share incentive plans	At or after age 62
Requirements of the Rule of Seventy	When an employee’s years of service with the Company (which must be at least 15 years) plus his or her age (which must be at least 55 years) on the date of termination equals or exceeds 70 years
Requirements of the Rule of Seventy for Executives	In the next two years: David J. Neithercut, Chief Executive Officer and President – 2011 and Alan George, Executive Vice President and Chief Investment Officer – 2013
Total compensation expense not yet vested	$ 19,500,000
Weighted average term for recognition of compensation expense not yet recognized (years)	1.5
Weighted average grant date fair value for Options	$ 6.18	$ 3.38	$ 4.08
Intrinsic value of options exercised	39,600,000	2,800,000	15,600,000
Fair value of restricted shares vested	9,100,000	8,000,000	23,900,000
Aggregate intrinsic value of options vested and expected to vest	184,300,000
Aggregate intrinsic value of options outstanding	184,300,000
Aggregate intrinsic value of options exercisable	117,100,000
Weighted average remaining contractual life in years of options exercisable	4.4
Market value of shares	$ 51.95
Options Exercisable	7,974,815	7,522,344
Weighted Average Exercise Price of Options Exercisable	$ 31.58	$ 28.45
Share options [Member]
Share based compensation arrangement by share based payment award
Restriction period of shares	3 years
Restricted shares [Member]
Share based compensation arrangement by share based payment award
Restriction period of shares	3 Years
Expiry period of options	10 years

Conversion rate of OP units (partnership interests) into common shares of company stock.

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Represents the closing share price of the company's stock on the balance sheet date.

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Maximum percentage of outstanding common shares that may be granted in the form of share options or restricted or non restricted shares under the company's share incentive plan.

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Maximum number of years an LTIP can remain outstanding and capital account of LTIP unit does not increase to a specified target within ten years, unit is cancelled.

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Number of installments in a vesting period.Each year, one-third of the total grant transfers ownership to each individual recipient. By the end of the third installment, the individual will have 100 % ownership of the full compensation.

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- Definition

Allows individual to combine years of service and age (70 years) to retire before age 62 and receive benefits under the company's share incentive plan..

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Number of years in which executives can be eligible to retire under the rule of 70.

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Period for each individual grant to be fully vested.

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Age at which an individual can retire and receive certain benefits under the company's share incentive plan.

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Share based compensation arrangement by share based payment award.

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Share incentive plans.

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As of the balance-sheet date, the aggregate unrecognized cost of share-based awards made to employees under share-based compensation plans that have yet to vest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
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The weighted average period over which unrecognized compensation is expected to be recognized for share-based compensation plans, using a decimal to express in number of years.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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- Definition

Reflects the dating as to when the share-based award expires as specified in the award agreement, which may be presented in a variety of ways (for example, year, month and year, day, month and year, quarter of a year).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Statement of Financial Accounting Standard (FAS)
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Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
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The total fair value of share-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares, other instruments, or cash in accordance with the terms of the arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph c(2)

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- Definition

The maximum number of shares originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the share-based compensation plan. As stock options and equity instruments other than options are awarded to participants, the shares remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
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- Definition

The difference between the maximum number of shares authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares already issued upon exercise of options or other share-based awards under the plan, and 2) shares reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance-sheet date.

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- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance-sheet date can be currently converted under the option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
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- Definition

The weighted average period between the balance-sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph c(2)

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
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- Definition

The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance-sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
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- Definition

As of the balance sheet date, the total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options that are exercisable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
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