Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation (Details)

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Stock Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense $ 0.9 $ 1.3 $ 4.0 $ 3.8
Restricted Share Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fair value of share grants vested     $ 2.6 $ 1.0
Total unvested restricted share awards (in shares) 209,560   209,560  
Weighted average grant date fair value (in dollars per share) $ 27.31   $ 27.31  
Total compensation costs, non-vested restricted share awards $ 2.4   $ 2.4  
Total compensation cost not yet recognized, period for recognition (in months)     20 months  
Washington Real Estate Investment Trust 2007 Omnibus Long-Term Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock based plan, aggregate number of shares authorized (in shares) 2,000,000   2,000,000  
Stock based plan, period in effect (in years)     10 years