Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation (Details)

v3.10.0.1
Stock Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 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 $ 1.7 $ 1.2 $ 5.1 $ 3.6  
Restricted Share Awards          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Fair value of share grants vested     $ 1.1 $ 2.0  
Total unvested restricted share awards (in shares) 479,262   479,262    
Weighted average grant date fair value (in dollars per share) $ 28.58   $ 28.58    
Total compensation costs, non-vested restricted share awards $ 9.1   $ 9.1    
Total compensation cost not yet recognized, period for recognition (in months)     28 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   2,400,000.0    
Stock based plan, period in effect (in years)     10 years