Summary of Significant Accounting Policies - Reclassification Out Of AOCI, Simon Property Group, L.P. (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)
Other Income.	90,563	90,161	286,491	219,796
Simon Property Group, L.P.
Significant Accounting Policies
Interest expense	(199,469)	(199,032)	(611,585)	(604,408)
Other Income.	$ 90,563	$ 90,161	286,491	219,796
Accumulated derivative gains (losses), net | Simon Property Group, L.P. | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Interest expense			$ (5,929)	(7,238)
Net unrealized losses on marketable securities | Simon Property Group, L.P. | Amount reclassified from accumulated other comprehensive income (loss)
Significant Accounting Policies
Other Income.				$ 21,541