Acquisitions (Details)	Aug. 23, 2019 USD ($) ft²	May 06, 2019 USD ($) ft²	Dec. 31, 2019 USD ($) ft² a
Business Acquisition [Line Items]
Rentable square feet | ft²			16,000,000.0
Area of land | a			11.7
Galleria 100
Business Acquisition [Line Items]
Ownership Percentage Acquired		100.00%
Rentable square feet | ft²		414,293
Percentage Leased as of Acquisition (Unaudited)		91.00%
Net Contractual Purchase Price | $		$ 95,100,000
Galleria 400 and 600
Business Acquisition [Line Items]
Ownership Percentage Acquired	100.00%
Rentable square feet | ft²	863,623
Percentage Leased as of Acquisition (Unaudited)	84.00%
Net Contractual Purchase Price | $	$ 231,200,000
Unsecured Debt | Line of Credit | Unsecured 500 Million 2018 Line Of Credit
Business Acquisition [Line Items]
Amount of line of credit | $			$ 500,000,000