Real Estate Transactions (Details) - Discontinued Operations, Disposed of by Sale ft² in Thousands, $ in Millions	1 Months Ended
	Mar. 31, 2020 USD ($) ft²	Feb. 29, 2020 USD ($) ft² a
Hearst Tower
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property | ft²	966
Gross sales price of property sold	$ 455.5
Gain on sale	$ 90.9
Woodcrest
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property | ft²		386
Gross sales price of property sold		$ 25.3
Downtown Atlanta
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property | a		8
Gross sales price of property sold		$ 13.3
Gain on sale		$ 13.1