Summary of Significant Accounting Policies - Noncontrolling Interests, Simon Property Group, Inc. (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Significant Accounting Policies
Limited partners' interests in the Operating Partnership	$ 503,972		$ 548,858
Nonredeemable noncontrolling interests in properties, net	3,632		3,738
Total noncontrolling interests reflected in equity	$ 507,604	$ 527,430	$ 552,596	$ 564,444	$ 621,738	$ 649,464