Impairment and Disposal of Long-Lived Assets - Assets Held for Sale (Details) $ in Thousands	Mar. 31, 2019 USD ($) bldg	Dec. 31, 2018 USD ($)
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Total assets held for sale	$ 423,846	$ 477,716
Liabilities held for sale	$ 18,035	17,065
Included in Continuing Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg	2
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	$ 2,444	1,301
Buildings and improvements	16,577	5,638
Land held for development	36,957	26,253
Accumulated depreciation	(2,814)	(1,546)
Deferred financing and leasing costs, net	382	58
Other assets	796	164
Total assets held for sale	54,342	31,868
Liabilities held for sale	$ 3,695	141
Included in Discontinued Operations
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg	16
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	$ 88,251	108,001
Buildings and improvements	297,375	371,461
Land held for development	0	0
Accumulated depreciation	(45,440)	(66,176)
Deferred financing and leasing costs, net	12,443	13,539
Other assets	16,875	19,023
Total assets held for sale	369,504	445,848
Liabilities held for sale	$ 14,340	16,924
Total
Balance Sheet Disclosures by Disposal Groups [Line Items]
Number of buildings (in buildings) | bldg	18
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Land and land improvements	$ 90,695	109,302
Buildings and improvements	313,952	377,099
Land held for development	36,957	26,253
Accumulated depreciation	(48,254)	(67,722)
Deferred financing and leasing costs, net	12,825	13,597
Other assets	17,671	19,187
Total assets held for sale	423,846	477,716
Liabilities held for sale	$ 18,035	$ 17,065