Dispositions and Held for Sale - Dispositions (Details) $ in Thousands	1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) outparcel	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) outparcel	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			$ 88,808			$ 88,808
Net Sales Price			87,315			87,315
Gain						8,246
Loss on impairment			(135,688)		$ (14,600)	(202,121)	$ (84,644)
Gain (loss) on sale of outparcels			$ 2,631			$ 4,731
Number of outparcels sold | outparcel			2			3
Gain (loss) related to land contributed			$ (187)			$ 433
Gain on Extinguishment of Debt			0		$ 0	71,722	0
Non-recourse loans on operating properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Balance of Non-recourse Debt			163,476			163,476
Gain on Extinguishment of Debt						71,722
Restatement Adjustment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sale of outparcels			602			588
Acadania Mall
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment								$ (1,593)	$ (43,007)
Non-cash default interest expense				$ 305
Proceeds from sale of real estate						4,000
Cary Towne Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment								$ (54,678)
Non-cash default interest expense				$ 237
Proceeds from sale of real estate						31,500
Malls
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment							$ (84,644)
Malls | Honey Creek Mall
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			14,600			14,600
Net Sales Price			14,360			14,360
Gain						0
Loss on impairment	$ (239)	$ (2,284)
Malls | Shops at Hickory Point
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			2,508			2,508
Net Sales Price			2,407			2,407
Gain						1,326
Malls | Acadania Mall | Non-recourse loans on operating properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Balance of Non-recourse Debt			119,760			119,760
Gain on Extinguishment of Debt						61,796
Malls | Cary Towne Center | Non-recourse loans on operating properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Balance of Non-recourse Debt			43,716			43,716
Gain on Extinguishment of Debt						9,926
All Other | Courtyard by Marriott at Pearland Town Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			15,100			15,100
Net Sales Price			14,795			14,795
Gain						1,910
All Other | 850 Greenbriar Circle
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			10,500			10,500
Net Sales Price			10,332			10,332
Gain						96
All Other | Kroger at Foothill Plaza
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			2,350			2,350
Net Sales Price			2,267			2,267
Gain						1,139
All Other | The Forum at Grandview
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			31,750			31,750
Net Sales Price			31,606			31,606
Gain						47
All Other | Barnes & Noble at High Point
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			2,000			2,000
Net Sales Price			1,899			1,899
Gain						821
All Other | Dick's Sporting Goods at Hanes Mall
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Sales Price			10,000			10,000
Net Sales Price			$ 9,649			9,649
Gain						$ 2,907