Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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-Article 12
-Section 13
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Fair Value Inputs, Capitalization Rate

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Fair Value Measurements.

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Provision For Asset Impairment, Properties Affected

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The charge against earnings resulting from the aggregate write down of assets from their carrying value to their fair value. Includes charges from both continued and discontinued operations.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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Amount after tax of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a discontinued operation.

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Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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Fair Value Measurements - Narrative (Details)	12 Months Ended
Fair Value Measurements - Narrative (Details)	Dec. 31, 2017 USD ($) Properties	Dec. 31, 2016 USD ($) Properties	Dec. 31, 2015 USD ($) Properties
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment	$ 27,754,000	$ 11,208,000	$ 108,154,000
Provision for asset impairment	27,754,000	117,722,000	108,154,000
Provision for asset impairment, discontinued operations	0		0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment	27,754,000	11,208,000	108,154,000
Investment properties, discontinued operations, total impairment loss	0	106,514,000	0
Fair Value, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Notional amount	150,000,000	150,000,000
Fair Value, Inputs, Level 3 [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Recurring fair value measurements	0	0
Retail [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment	$ 27,754,000	$ 11,208,000	15,987,000
Continuing Operations [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment			$ 92,167,000
Discontinued Operations [Member] \| Maximum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discount rates		15.25%
Fair value inputs, capitalization rate		10.00%
Discontinued Operations [Member] \| Minimum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discount rates		7.75%
Fair value inputs, capitalization rate		6.75%
Real Estate [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Discounted cash flow method, term			10 years
Real Estate [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Maximum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, capitalization rates	8.00%	7.00%	8.75%
Investment properties, discount rates	9.00%	8.00%	10.75%
Real Estate [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Minimum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, capitalization rates	7.00%	6.00%	7.50%
Investment properties, discount rates	8.00%	7.00%	8.00%
Real Estate [Member] \| Retail [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment, properties affected \| Properties	6	3	2
Mortgages [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discount rates	4.20%	5.07%
Line of Credit and Term Loan [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discount rates	3.48%	3.15%
Downtown Railyard Venture, LLC [Member] \| Continuing Operations [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discount rates			14.00%
Real Estate [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Provision for asset impairment		$ 29,931,000
Real Estate [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Maximum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, capitalization rates		7.00%
Investment properties, discount rates		8.00%
Real Estate [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Minimum [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, capitalization rates		6.75%
Investment properties, discount rates		7.00%
Spin-Off of Highlands REIT Inc. [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Fair Value Measurements (Additional Textual) [Abstract]
Investment properties, discontinued operations, total impairment loss		$ 76,583,000