Disposed Properties - Schedule of Disposal Groups (Details) $ in Thousands				12 Months Ended
	Jun. 26, 2018 USD ($)	Mar. 21, 2018 USD ($)	May 17, 2017 USD ($)	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($) ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross Disposition Price				$ 466,175	$ 244,066	$ 1,924,350
Gain (Loss) on Extinguishment of Debt				$ 9,103	$ 840	$ (10,498)
Retail
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				9,500,000	12,400,000	12,200,000
Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				3,481,000	1,558,000
Gross Disposition Price				$ 466,175	$ 190,566
Gain (Loss) on Sale and Transfer of Investment Properties, net				95,097	24,066
Gain (Loss) on Extinguishment of Debt				$ 9,157	$ 840
Sherman Town Center I & II \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				485,000
Gross Disposition Price				$ 63,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				12,382
Gain (Loss) on Extinguishment of Debt				$ 0
Grafton Commons \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				239,000
Gross Disposition Price				$ 33,500
Gain (Loss) on Sale and Transfer of Investment Properties, net				6,564
Gain (Loss) on Extinguishment of Debt				$ 0
Lakeport Commons \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				283,000
Gross Disposition Price				$ 31,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				(666)
Gain (Loss) on Extinguishment of Debt				$ 0
Stonecrest Marketplace \| Retail \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				265,000
Gross Disposition Price				$ 0
Gain (Loss) on Sale and Transfer of Investment Properties, net		$ 1,777		1,777
Gain (Loss) on Extinguishment of Debt				$ 10,752
Carrying value, surrendered properties		$ 23,932
Northwest Marketplace \| Retail \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Condemnation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				0
Gross Disposition Price				$ 0
Gain (Loss) on Sale and Transfer of Investment Properties, net				248
Gain (Loss) on Extinguishment of Debt				$ 0
Market at Morse/Hamilton \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				45,000
Gross Disposition Price				$ 10,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				1,592
Gain (Loss) on Extinguishment of Debt				$ 0
Siegen Plaza \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				156,000
Gross Disposition Price				$ 29,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				3,849
Gain (Loss) on Extinguishment of Debt				$ (54)
Tomball Town Center \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				67,000
Gross Disposition Price				$ 22,750
Gain (Loss) on Sale and Transfer of Investment Properties, net				7,184
Gain (Loss) on Extinguishment of Debt				$ 0
Bellerive Plaza \| Retail \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				76,000
Gross Disposition Price				$ 0
Gain (Loss) on Sale and Transfer of Investment Properties, net	$ (22)			(22)
Gain (Loss) on Extinguishment of Debt				$ 1,694
Carrying value, surrendered properties	$ 4,771
Parkway Centre North \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				143,000
Gross Disposition Price				$ 23,700
Gain (Loss) on Sale and Transfer of Investment Properties, net				5,357
Gain (Loss) on Extinguishment of Debt				$ (1,695)
Tulsa Hills \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				473,000
Gross Disposition Price				$ 70,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				13,476
Gain (Loss) on Extinguishment of Debt				$ 0
McKinney Town Center \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				243,000
Gross Disposition Price				$ 51,000
Gain (Loss) on Sale and Transfer of Investment Properties, net				15,430
Gain (Loss) on Extinguishment of Debt				$ 0
Riverstone Shopping Center \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				273,000
Gross Disposition Price				$ 27,750
Gain (Loss) on Sale and Transfer of Investment Properties, net				(320)
Gain (Loss) on Extinguishment of Debt				$ (1,540)
Hiram Pavilion \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				363,000
Gross Disposition Price				$ 44,350
Gain (Loss) on Sale and Transfer of Investment Properties, net				22,124
Gain (Loss) on Extinguishment of Debt				$ 0
Poplin Place \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				228,000
Gross Disposition Price				$ 28,300
Gain (Loss) on Sale and Transfer of Investment Properties, net				2,841
Gain (Loss) on Extinguishment of Debt				$ 0
Walden Park \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				34,000
Gross Disposition Price				$ 5,325
Gain (Loss) on Sale and Transfer of Investment Properties, net				5
Gain (Loss) on Extinguishment of Debt				$ 0
Streets of Cranberry \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²				108,000
Gross Disposition Price				$ 26,500
Gain (Loss) on Sale and Transfer of Investment Properties, net				3,276
Gain (Loss) on Extinguishment of Debt				0
Additional Loan \| Retail
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Extinguishment of Debt				$ (4)
Penn Park \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					242,000
Gross Disposition Price					$ 29,050
Gain (Loss) on Sale and Transfer of Investment Properties, net					1,021
Gain (Loss) on Extinguishment of Debt					$ 0
Intech Retail \| Retail \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					0
Gross Disposition Price					$ 0
Gain (Loss) on Sale and Transfer of Investment Properties, net			$ (52)		(52)
Gain (Loss) on Extinguishment of Debt					$ 882
Carrying value, surrendered properties			$ 2,338
Sparks Crossing \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					336,000
Gross Disposition Price					$ 40,280
Gain (Loss) on Sale and Transfer of Investment Properties, net					10,559
Gain (Loss) on Extinguishment of Debt					$ 0
Lincoln Village \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					164,000
Gross Disposition Price					$ 30,000
Gain (Loss) on Sale and Transfer of Investment Properties, net					2,355
Gain (Loss) on Extinguishment of Debt					$ 0
Market at Westlake \| Retail \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Condemnation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					0
Gross Disposition Price					$ 0
Gain (Loss) on Sale and Transfer of Investment Properties, net					473
Gain (Loss) on Extinguishment of Debt					$ 0
Pavilions at Hartman Heritage \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					223,000
Gross Disposition Price					$ 21,700
Gain (Loss) on Sale and Transfer of Investment Properties, net					(1,736)
Gain (Loss) on Extinguishment of Debt					$ 0
Legacy Crossing \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					134,000
Gross Disposition Price					$ 10,250
Gain (Loss) on Sale and Transfer of Investment Properties, net					(211)
Gain (Loss) on Extinguishment of Debt					$ (1)
Heritage Plaza \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					132,000
Gross Disposition Price					$ 21,350
Gain (Loss) on Sale and Transfer of Investment Properties, net					9,189
Gain (Loss) on Extinguishment of Debt					$ (41)
Crossroads at Chesapeake \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					0
Gross Disposition Price					$ 1,250
Gain (Loss) on Sale and Transfer of Investment Properties, net					834
Gain (Loss) on Extinguishment of Debt					$ 0
Scofield Crossing \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					0
Gross Disposition Price					$ 2,936
Gain (Loss) on Sale and Transfer of Investment Properties, net					2,247
Gain (Loss) on Extinguishment of Debt					$ 0
Dothan Plaza \| Retail \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square Feet \| ft²					327,000
Gross Disposition Price					$ 33,750
Gain (Loss) on Sale and Transfer of Investment Properties, net					(613)
Gain (Loss) on Extinguishment of Debt					$ 0