Basis of Presentation, Consolidation, Investments in Joint Ventures, and Noncontrolling Interests - Investment Properties (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Land, buildings and improvements	$ 3,670,110	$ 3,873,149
Furniture, equipment and other	9,022	8,453
Land held for development	31,142	31,142
Construction in progress	43,692	45,140
Investment properties, at cost	$ 3,753,966	$ 3,957,884