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Stock Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 2.1	$ 1.7	$ 5.9	$ 6.3
Restricted Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of share awards vested			$ 0.8	$ 1.7
Total unvested restricted share awards (in shares)	502,300		502,300
Weighted average grant date fair value (in dollars per share)	$ 29.99		$ 29.99
Total compensation cost related to unvested restricted share awards	$ 8.7		$ 8.7
Total compensation cost related to unvested restricted share awards, expected period for recognition (in months)			23 months
Washington Real Estate Investment Trust 2016 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of shares authorized for stock based awards (in shares)	2,400,000		2,400,000
Stock based plan, period in effect (in years)			10 years
Officer LTIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate weighting of performance and time-based measures (percent)	100.00%		100.00%
Officer LTIP \| Time-based award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			3 years
Vesting percentage per year over three-year vesting period (percent)			33.33%
Officer LTIP \| Performance award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of awards that vest immediately after performance period (percent)	100.00%		100.00%