The Combination Fair Value of Tangible and Identified Intangible Assets and Liabilities (Details) - JBG Companies [Member] $ in Thousands	Jul. 18, 2017 USD ($)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings and Improvements	$ 543,584
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tenant Improvements	65,572
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings	609,156
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Leasehold Improvements	4,422
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Equipment	3,468
Business Combination, Recognized Identifiable Assets and Assumed Liabilities, Leasehold Improvements and Equipment	$ 7,890
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years 3 months 18 days
Identified intangible assets	$ 138,371
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Liabilities	8,687
In-place lease amortization (1)
Finite-lived Intangible Assets Acquired	$ 60,317
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 4 months 24 days
Above-market real estate lease amortization (2)
Finite-lived Intangible Assets Acquired	$ 11,732
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 3 months 18 days
Below-market ground lease amortization (3)
Finite-lived Intangible Assets Acquired	$ 332
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	88 years 6 months
Option to enter into ground lease amortization (3)
Finite-lived Intangible Assets Acquired	$ 17,090
Management and leasing contract amortization (1)
Finite-lived Intangible Assets Acquired	$ 48,900
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years 6 months
Minimum | Leasing Arrangement [Member]
Finite-Lived Intangible Asset, Useful Life	3 years
Maximum | Leasing Arrangement [Member]
Finite-Lived Intangible Asset, Useful Life	9 years
Building and Building Improvements [Member] | Minimum
Property, Plant and Equipment, Useful Life	3 years
Building and Building Improvements [Member] | Maximum
Property, Plant and Equipment, Useful Life	40 years
Equipment [Member]
Property, Plant and Equipment, Useful Life	5 years