Co-Venture Arrangement - Schedule of Co-venture Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Co-Venture Arrangement
Liability—Co-venture obligation	$ 0	$ 58,973
Freehold Raceway Mall and Chandler Fashion Center | Joint venture
Co-Venture Arrangement
Investments in unconsolidated joint ventures	$ 31,150	0
Liability—Co-venture obligation		$ 58,973