Transactions with Norfolk Southern Railway Company (Additional Information) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Mar. 01, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property		$ 57,676	$ 0
Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property purchased		6,500		$ 37,000
Site Preparation Work
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property purchased		4,000
NS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transaction price	$ 52,300
NS | 1200 Peachtree
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase of a building	$ 82,000
Lease term	3 years
Impairment of property	$ 10,300
NS | Fees for development services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract fees	5,000
NS | Fees for consulting services
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract fees	32,000
NS | Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of property	52,500
Gain from sale of property	$ 5,000
NS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue recognized		$ 6,600