Mortgage and Other Notes Receivable - Summary (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Assignment of the partnership interest (as a percent)		100.00%
Mortgage and Other Notes Receivable [Line Items]
Balance	[1]	$ 8,171	$ 8,945
Mortgages
Mortgage and Other Notes Receivable [Line Items]
Balance		$ 5,189	$ 5,418
Mortgages | Columbia Place Outparcel
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		5.00%	5.00%
Balance		$ 288	$ 302
Mortgages | One Park Place
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		5.00%	5.00%
Balance		$ 837	$ 1,010
Mortgages | Village Square
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		4.00%	4.00%
Balance		$ 1,554	$ 1,596
Mortgages | Other
Mortgage and Other Notes Receivable [Line Items]
Balance		$ 2,510	$ 2,510
Mortgages | Other | Minimum
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		4.73%	4.07%
Mortgages | Other | Maximum
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		9.50%	9.50%
Mortgages | The Promenade at Dlberville
Mortgage and Other Notes Receivable [Line Items]
Balance		$ 1,100
Other Notes Receivable
Mortgage and Other Notes Receivable [Line Items]
Balance		$ 2,982	$ 3,527
Other Notes Receivable | ERMC
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		4.00%	4.00%
Balance		$ 2,354	$ 2,855
Other Notes Receivable | Southwest Theaters LLC
Mortgage and Other Notes Receivable [Line Items]
Interest Rate (as a percent)		5.00%	5.00%
Balance		$ 628	$ 672

[1] As of September 30, 2018, includes $621,616 of assets related to consolidated variable interest entities that can be used only to settle obligations of the consolidated variable interest entities and $414,923 of liabilities of consolidated variable interest entities for which creditors do not have recourse to the general credit of the Company. See Note 6.