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

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The weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, using a decimal to express in number of years.

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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).

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding 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

-Subparagraph b(2)(a)

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-Section 50

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The liabilities paid during the accounting period for equity-based compensation.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The total fair value of equity-based awards for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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.

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

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

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-Topic 718

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-Section 50

-Paragraph 2

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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.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)-(ii)

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-Topic 718

-SubTopic 10

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64

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-Paragraph 2

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

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- Definition

The weighted-average period remaining as of the balance sheet date until option expiration pertaining to the outstanding stock options for all option plans in the customized range of exercise prices, which may be expressed in a variety of ways (for example, years, months).

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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Number of share options (or share units) exercised during the current period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

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-Name Regulation S-X (SX)

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-Subparagraph (SX 210.3-04)

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Future Expected Expense with Performance Conditions Expected To Be Awarded

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Number of Restricted Shares Subsequent to Adoption of New share-based Compensation Plan

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Percentage Of Awards Earned

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- Definition

Percentage Of Cash Portion Related To Deferred Compensation Plan

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Percentage Of Deferred Amounts In Restricted Cash

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Percentage Of Potential Award Depend Upon Market Condition

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Percentage Of Restricted Shares Subject To Performance Conditions

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Remaining unvested restricted shares granted

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Share Based Compensation Arrangement By Share Based Payment Award Award Performance Period.

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Share based compensation arrangement by share based payment award equity instruments other than options nonvested total intrinsic value.

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Share-based compensation arrangement by share-based payment award fair value restricted shares at grant date

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Stock based plan, period in effect (in years)

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Weighted Average Period Of Cost Recognition

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Weighted Average Period Of Unamortized Value Recognition

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Stock Based Compensation (Narrative) (Details) (USD $)	9 Months Ended											0 Months Ended	9 Months Ended				3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended
Stock Based Compensation (Narrative) (Details) (USD $)	Sep. 30, 2011 New STIP [Member]	Sep. 30, 2011 New STIP [Member] Performance-Based Awards [Member]	Sep. 30, 2011 New STIP [Member] Performance-Based Awards [Member] Cash [Member]	Sep. 30, 2011 New STIP [Member] Performance-Based Awards [Member] Restricted Share Units [Member]	Sep. 30, 2011 New STIP [Member] Service-Based Awards [Member]	Sep. 30, 2011 New STIP [Member] Service-Based Awards [Member] Restricted Share Units [Member]	Sep. 30, 2011 New LTIP [Member]	Sep. 30, 2011 New LTIP [Member] Restricted Share Units [Member]	Sep. 30, 2011 New LTIP [Member] Unrestricted Share Units [Member]	Sep. 30, 2011 New LTIP [Member] Restricted Share Awards [Member]	Sep. 30, 2011 New LTIP [Member] Unrestricted Share Awards [Member]	Feb. 17, 2011 Prior LTIP [Member]	Sep. 30, 2011 Prior LTIP [Member]	Sep. 30, 2011 Washington Real Estate Investment Trust 2007 Omnibus Long-Term Incentive Plan [Member]	Sep. 30, 2011 Vest On December 31, 2011 [Member] Restricted Share Units [Member]	Sep. 30, 2011 Vest On December 31, 2012 [Member] Restricted Share Units [Member]	Sep. 30, 2011 Restricted And Unrestricted Shares [Member]	Sep. 30, 2011 Restricted And Unrestricted Shares [Member] months	Sep. 30, 2011 Options [Member] years	Sep. 30, 2011 Restricted Share Units [Member]	Sep. 30, 2011 Restricted Share Units [Member]	Sep. 30, 2011 Restricted Share Awards [Member]	Sep. 30, 2011 Unrestricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based plan, aggregate number of shares authorized														2,000,000
Stock based plan, period in effect (in years)														10
Percentage of awards earned			50.00%	50.00%		15.00%		50.00%	50.00%
Performance period (years)	1						3
Vesting period (in years)	four	three			three			one					five
Percentage of cash portion pursuant to deferred compensation plan	80.00%
Percentage of deferred amounts in restricted cash	25.00%
Percentage of restricted shares subject to performance conditions	20.00%						60.00%
Percentage of potential award depend upon market condition							40.00%
Length of compensation expense recognition period (in years)										4	3		6
Number of restricted shares subsequent to adoption of new share-based compensation plan												154,400
Options outstanding																			103,102
Exercise price, minimum																			$ 24.85
Exercise price, maximum																			$ 33.09
Weighted average exercise price, options outstanding																			$ 27.31
Weighted average remaining contractual term, options outstanding (years)																			1.6
Aggregate intrinsic value of outstanding exercisable shares																			$ 100,000
Options exercised																			42,883
Aggregate intrinsic value of options exercised																			200,000
Total Fair value of vested shares																		28,800		0	247,100
Shares vested																	0	0
Remaining unvested restricted shares granted													0					0
Value of unvested restricted share units																					4,100,000
Weighted average period of recognition, compensation cost (months)																		27			27
Restricted shares granted during the period																		10,822
Fair value at grant date																	300,000	300,000
Unamortized value of unvested share awards																	265,600	265,600
Compensation cost of restricted shares																	600,000	600,000
Weighted average period of recognition, unamortized value (months)																		28			28	39	27
Total number of share units awarded															89,000	65,400
Future expected expense expected to be awarded to non-officers																					$ 800,000