Summary of Significant Accounting Policies - Reclassification Out of AOCI, Simon Property Group, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Significant Accounting Policies
Interest expense	$ (199,469)	$ (199,032)	$ (611,585)	$ (604,408)
Net income attributable to noncontrolling interests	(85,111)	(78,018)	(262,722)	(209,070)
Other Income.	90,563	90,161	286,491	219,796
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS or UNITHOLDERS	$ 556,267	$ 513,783	1,723,925	1,373,509
Accumulated derivative losses, net, including noncontrolling interests | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Interest expense			(5,929)	(7,238)
Accumulated derivative losses, attributable to noncontrolling interests | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Net income attributable to noncontrolling interests			785	955
Accumulated derivative gains (losses), net | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS or UNITHOLDERS			$ (5,144)	(6,283)
Realized gains on sales of marketable securities, including Portion Attributable to Noncontrolling Interest | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Other Income.				21,541
Realized gains on sales of marketable securities, attributable to Noncontrolling Interest | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Net income attributable to noncontrolling interests				(2,843)
Net unrealized losses on marketable securities | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS or UNITHOLDERS				$ 18,698