Impairment and Disposal of Long-Lived Assets - Assets Held for Sale (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Sep. 30, 2019 a	Sep. 30, 2019 properties	Sep. 30, 2019 bldg	Dec. 31, 2018 USD ($)
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Total assets held for sale	$ 226,504				$ 502,207
Liabilities held for sale	15,939				21,131
Included in Continuing Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg				1
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	613				1,301
Buildings and improvements	8,541				5,638
Disposal Group, Including Discontinued Operation, Development in Progress	0				0
Land held for development	19,420				26,253
Accumulated depreciation	(3,745)				(1,546)
Deferred financing and leasing costs, net	717				58
Other assets	756				164
Total assets held for sale	26,302				31,868
Liabilities held for sale	419				141
Included in Discontinued Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg				9
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	19,210				113,080
Buildings and improvements	174,595				384,737
Disposal Group, Including Discontinued Operation, Development in Progress	10,108				9,597
Land held for development	0				0
Accumulated depreciation	(21,592)				(70,242)
Deferred financing and leasing costs, net	7,910				13,697
Other assets	9,971				19,470
Total assets held for sale	200,202				470,339
Liabilities held for sale	15,520				20,990
Total
Balance Sheet Disclosures by Disposal Groups [Line Items]
Acres of Developable Land (in acres) | a		74.4
Number of buildings (in buildings)			3	10
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	19,823				114,381
Buildings and improvements	183,136				390,375
Disposal Group, Including Discontinued Operation, Development in Progress	10,108				9,597
Land held for development	19,420				26,253
Accumulated depreciation	(25,337)				(71,788)
Deferred financing and leasing costs, net	8,627				13,755
Other assets	10,727				19,634
Total assets held for sale	226,504				502,207
Liabilities held for sale	$ 15,939				$ 21,131