Discontinued Operations - Additional Information (Details) $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 09, 2018 shares	Jul. 05, 2017 shares	Aug. 31, 2017 USD ($) ft² property	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment of Select Income REIT investment				$ 0	$ 15,180	$ 0
Net book value				$ 3,105,575	3,569,489
Falls Church, VA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties | property			1
Rentable area of properties (in square feet) | ft²			164,746
Net book value			$ 12,901
Aggregate sale price of properties sold, excluding closing costs			$ 13,523
Underwritten Public Offering
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of shares sold (in shares) | shares		6,250,000
Common Shares | Underwritten Public Offering
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of shares sold (in shares) | shares	24,918,421
Loss on impairment of Select Income REIT investment					$ 18,665