Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation (Details)

v3.8.0.1
Stock Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percent of relative TSR evaluated relative to peer companies 50.00%   50.00%
Percent of relative TSR evaluated relative to FTSE NAREIT Diversified Index 50.00%    
Percent of absolute TSR evaluated     50.00%
Performance period per amendment 3 years    
Stock based compensation expense $ 1.5 $ 1.1  
Restricted Share Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of share grants vested $ 0.7 $ 1.6  
Total unvested restricted share awards (in shares) 481,116    
Weighted average grant date fair value (in dollars per share) $ 28.57    
Total compensation costs, non-vested restricted share awards $ 11.8    
Total compensation cost not yet recognized, period for recognition (in months) 32 months    
Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock based plan, aggregate number of shares authorized (in shares) 2,400,000.0    
Stock based plan, period in effect (in years) 10 years