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Area of land held.

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Real Estate (Significant Dispositions) (Details)			1 Months Ended	3 Months Ended	9 Months Ended
Real Estate (Significant Dispositions) (Details)	Aug. 16, 2018 USD ($)	Jun. 15, 2018 USD ($) a ft²	Aug. 31, 2018 USD ($)	Sep. 30, 2018 USD ($) condominiums	Sep. 30, 2018 USD ($) condominiums	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Significant Acquisition and Dispositions
Distribution from real estate partnership in excess of earnings					$ 237,000	$ 1,672,000
Our investment in joint venture				$ 27,647,000	27,647,000		$ 23,941,000
Assets held for sale				21,990,000	21,990,000		$ 0
Jordan Downs Plaza
Significant Acquisition and Dispositions
Square footage of real estate property \| ft²		113,000
Construction pre-funding investment		$ 34,400,000
Controlling interest percentage		91.00%
Land parcel acre on which the shopping center will be constructed \| a		9.4
Contributions from a third party bank		$ 13,900,000
Strike price of put option		1,000
Direct and incremental costs of structuring the NMTC transaction		$ 1,600,000
Cash in escrow to be used for development				39,700,000	39,700,000
Assembly Row Hotel \| Hotel \| Equity Method Investment
Significant Acquisition and Dispositions
Contribution of Property			$ 44,000,000
Distribution from real estate partnership in excess of earnings			$ 38,000,000
Our investment in joint venture				$ 5,600,000	$ 5,600,000
Chelsea Commons \| Residential
Significant Acquisition and Dispositions
Proceeds from sale	$ 15,000,000
Gain on sale	$ 3,100,000
Assembly Row and Pike & Rose \| Condominiums
Significant Acquisition and Dispositions
Number of condominium units sold \| condominiums				8	167
Proceeds from sale				$ 6,700,000	$ 128,100,000
Gain on sale					7,300,000
Taxes related to the sale of condominiums					1,700,000
Assets held for sale				$ 22,000,000	$ 22,000,000