Acquisitions (Details)	Aug. 23, 2019 USD ($) ft²	May 06, 2019 USD ($) ft²	Sep. 30, 2019 USD ($) a property
Property, Plant and Equipment [Line Items]
Number of properties acquired | property			3
Area of land acquired (in acres) | a			11.7
$500 Million Unsecured 2018 Line of Credit | Unsecured Debt
Property, Plant and Equipment [Line Items]
Face amount of debt instrument			$ 500,000,000
Galleria 100
Property, Plant and Equipment [Line Items]
Ownership percentage acquired		100.00%
Rentable square feet (in sq ft) | ft²		414,293
Percentage leased		91.00%
Net contractual purchase price		$ 95,100,000
Galleria 400 and 600
Property, Plant and Equipment [Line Items]
Ownership percentage acquired	100.00%
Rentable square feet (in sq ft) | ft²	863,623
Percentage leased	84.00%
Net contractual purchase price	$ 231,200,000