Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Period 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, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section D
-Subsection 2

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Capitalized Share-based Compensation During Period

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Closing Share Price, Date of Grant

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Grant Date Fair Value as a Percentage of Base Salary

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Grant Date Fair Value as a Percentage of Base Salary on absolute TSR

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Grant Date Fair Value as a Percentage of Base Salary on relative TSR

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- Definition

Percentage Payable in Restricted Shares

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Percentage Payable In Unrestricted Shares

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Percentage of Potential Award Based Upon Service Requirement

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Share-based Compensation Arrangement by Share-based Payment Award, Plan in Effect, Period

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Share-based Compensation Arrangements by Share-based Payment Awards, Options, Vested after Performance Period, Percentage

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- Definition

Trustee Share-based Compensation

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Weighting for Performance Measurement Based on 20 Peer Comapnies

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Weighting for Performance Measurement Based on Cumulative 3-Year Total Shareholder Return

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Stock Based Compensation - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 23, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Trustee share-based compensation	$ 100,000	$ 55,000	$ 55,000
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost	5,100,000	5,000,000	6,200,000
Capitalized Share-based Compensation During Period	600,000
Fair value of restricted share units vested	$ 5,800,000	$ 6,100,000	3,800,000
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	20 months
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 1,800,000
Washington Real Estate Investment Trust 2007 Omnibus Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	2,000,000
Plan in effect, period	10 years
Options outstanding	0
New STIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Potential Award Based Upon Service Requirement	50.00%
Awards, Vested after Performance Period, Percentage	50.00%
Performance period	1 year
New STIP [Member] \| Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	75.00%
Percentage payable in restricted shares	25.00%
Award vesting period	3 years
Performance period	3 years
Total compensation cost not yet recognized, period for recognition	4 years
Grant date fair value as a percentage of base salary	150.00%
Weighting for performance measurement based on cumulative 3-Year total shareholder return	50.00%
Weighting for performance measurement based on 20 peer comapnies	50.00%
Fair value assumptions, expected volatility rate		23.20%
Fair value assumptions, risk free interest rate		0.80%
Closing share price, date of grant				$ 24.08
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	50.00%	50.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	50.00%	50.00%
New LTIP [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value as a percentage of base salary	80.00%
Fair value assumptions, expected volatility rate	17.20%
Fair value assumptions, risk free interest rate	1.00%
Fair value assumptions, expected term	3 years	3 years
Closing share price, date of grant	$ 27.66
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	15.00%	20.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	36.00%	35.00%
New LTIP [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value assumptions, expected volatility rate	17.50%
Fair value assumptions, risk free interest rate	1.10%
Fair value assumptions, expected term	4 years	4 years
Closing share price, date of grant	$ 27.76
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR	29.00%	38.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR	69.00%	67.00%
Cash [Member] \| New STIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	100.00%
Cash [Member] \| New STIP [Member] \| Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable In unrestricted shares	50.00%
Unrestricted Share Awards [Member] \| New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	3 years
Restricted Share Units [Member] \| New STIP [Member] \| Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage payable in restricted shares	50.00%
Restricted Share Units [Member] \| New LTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period	1 year
Restricted Share Units [Member] \| New LTIP [Member] \| Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation cost not yet recognized, period for recognition	4 years
Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost			$ 1,000,000
One Year [Member] \| New LTIP [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR		10.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR		11.00%
One Year [Member] \| New LTIP [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR		20.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR		20.00%
Two Year [Member] \| New LTIP [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR		16.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR		23.00%
Two Year [Member] \| New LTIP [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value as a Percentage of Base Salary on absolute TSR		30.00%
Grant Date Fair Value as a Percentage of Base Salary on relative TSR		43.00%