Transactions with Norfolk Southern Railway Company - Additional Information (Details) - USD ($)		12 Months Ended
	Mar. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property		$ 435,833,000	$ 62,667,000	$ 372,000
Total Assets		7,107,398,000	7,151,447,000
Contract price that is expected to be recognized as revenue	$ 52,300,000
Deferred income		62,319,000	52,269,000
NS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue recognized		14,900,000	21,400,000
Deferred income		$ 5,700,000	11,300,000
1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total 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 | 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	5,000,000.0
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	32,000,000.0
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	$ 5,000,000.0