Summary of Significant Accounting Policies - Noncontrolling Interests, Simon Property Group, Inc. (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies
Limited partners' interests in the Operating Partnership	$ 548,858	$ 644,348
Nonredeemable noncontrolling interests in properties, net	3,738	5,116
Total noncontrolling interests reflected in equity	$ 552,596	$ 649,464	$ 744,905	$ 858,328