Transactions with Norfolk Southern Railway Company (Additional Information) (Details) - USD ($)		12 Months Ended
	Mar. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property		$ 62,667,000	$ 372,000	$ 370,944,000
Assets		7,151,447,000	4,146,296,000
Contract price that is expected to be recognized as revenue	$ 52,300,000
Deferred income		52,269,000	41,266,000
1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets	92,300,000
Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property purchased		6,500,000	$ 37,000,000.0
Site Preparation Work
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property purchased	4,000,000.0
NS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue recognized		21,400,000
Deferred income		$ 11,300,000
NS | 1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase of a building	$ 82,000,000
Lease term	3 years
Discount on service contract price	$ 10,300,000
Gain or loss on derecognition of non financial asset fair value	0
Consideration for the various services component	52,300,000
NS | Fees for development services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract fees	5,000,000
NS | Fees for consulting services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract fees	32,000,000
NS | Development agreement | 1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration for various services contract	5,000,000
NS | Consulting agreement | 1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration for various services contract	32,000,000
NS | Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property	52,500,000
Gain on sale of property	5,000,000.0
NS | Land | 1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration for various services contract	$ 5,000,000