Stock Based Compensation (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended			12 Months Ended														0 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Feb. 17, 2011	Dec. 31, 2011 New LTIP [Member] Y	Dec. 31, 2010 New LTIP [Member]	Dec. 31, 2011 Washington Real Estate Investment Trust 2007 Omnibus Long-Term Incentive Plan [Member] years	Dec. 31, 2011 New STIP [Member] Y	Dec. 31, 2011 New STIP [Member] Performance-Based Awards [Member]	Dec. 31, 2011 New STIP [Member] Service-Based Awards [Member]	Dec. 31, 2011 New STIP [Member] Cash [Member] Performance-Based Awards [Member]	Dec. 31, 2011 New STIP [Member] Restricted Share Units [Member] Performance-Based Awards [Member]	Dec. 31, 2011 New STIP [Member] Restricted Share Units [Member] Service-Based Awards [Member]	Dec. 31, 2011 New LTIP [Member] Y	Dec. 31, 2011 New LTIP [Member] Minimum [Member]	Dec. 31, 2011 New LTIP [Member] Maximum [Member]	Dec. 31, 2011 New LTIP [Member] Unrestricted Share Units [Member]	Dec. 31, 2011 New LTIP [Member] Restricted Share Units [Member]	Dec. 31, 2011 New LTIP [Member] Restricted Share Units [Member]	Dec. 31, 2011 New LTIP [Member] Restricted Share Units [Member] Performance-Based Awards [Member] Y	Dec. 31, 2011 New LTIP [Member] Unrestricted Share Awards [Member] Y	Feb. 17, 2011 Prior LTIP [Member]	Dec. 31, 2010 Prior LTIP [Member]	Dec. 31, 2011 Prior LTIP [Member] Restricted Share Units [Member] Officer [Member] Y	Dec. 31, 2010 Prior LTIP [Member] Restricted Share Units [Member] Officer [Member]	Dec. 31, 2011 Management [Member] Prior LTIP [Member] Restricted Share Units [Member] Y	Dec. 31, 2010 Management [Member] Prior LTIP [Member] Restricted Share Units [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
Expected volatility	58.10%
Risk Free Interest Rate	1.20%
Closing Share Price, Date of Grant				$ 30.91
Percentage Of Awards Earned												50.00%			65.00%	150.00%	50.00%	50.00%
Percentage of Base Salary Used to Determine Grant Date Fair Value															79.00%	185.00%
Expected life (from grant date)					3	4
Share Based Compensation Arrangement By Share Based Payment Award Award Performance Period								1						3												1
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition					4					3										4	3			5		6
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period								4	3	3									1
Percentage Payable In Unrestricted Shares											50.00%							50.00%
Percentage of Awards Earned													15.00%
Percentage Of Cash Portion Related To Deferred Compensation Plan								80.00%
Percentage Of Potential Award Depend Upon Market Condition														40.00%
Percentage of Potential Award Based Upon Strategic Plan Fulfillment														60.00%
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%
Percentage Of Deferred Amounts In Restricted Cash								25.00%
Percentage Of Restricted Shares Subject To Performance Conditions								20.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period, Maximum						3																			5		5
Number of Restricted Shares Subsequent to Adoption of New share-based Compensation Plan																						154,400
Number of Restricted Shares Previously Granted and Nonvested																							59,100
Trustee Share-based Compensation	$ 55,000	$ 55,000	$ 55,000
Stock-based compensation expense	$ 5,600,000	$ 5,900,000	$ 3,500,000