Co-Venture Arrangement - Narrative (Details) ft² in Thousands	Sep. 30, 2009 USD ($) ft²	Dec. 31, 2017 USD ($)	Oct. 19, 2017 USD ($)	Dec. 31, 2016 USD ($)
Co-Venture Arrangement
Co-venture obligation		$ 0		$ 58,973,000
Freehold Raceway Mall loan | Joint venture
Co-Venture Arrangement
Mortgage loan			$ 400,000,000
Freehold Raceway Mall and Chandler Fashion Center
Co-Venture Arrangement
Ownership interest (as a percent)	49.90%
Co-venture obligation	$ 168,154,000
Freehold Raceway Mall
Co-Venture Arrangement
Property square footage | ft²	1,671
Chandler Fashion Center
Co-Venture Arrangement
Property square footage | ft²	1,318