Summary of Significant Accounting Policies - AOCI, Simon Property Group L.P. (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Simon Property Group, L.P.
Changes in accumulated other comprehensive income (loss)
Beginning Balance	$ 4,235,026
Ending balance	3,893,559
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss)
Other comprehensive (loss) income before reclassifications	(13,284)
Amounts reclassified from accumulated other comprehensive income (loss)	5,144
Net current-period other comprehensive (loss) income	(8,140)
Accumulated Other Comprehensive Income (Loss) \| Simon Property Group, L.P.
Changes in accumulated other comprehensive income (loss)
Beginning Balance	(127,102)
Other comprehensive (loss) income before reclassifications	(15,530)
Amounts reclassified from accumulated other comprehensive income (loss)	5,929
Net current-period other comprehensive (loss) income	(9,601)
Ending balance	(136,703)
Currency translation adjustments
Changes in accumulated other comprehensive income (loss)
Other comprehensive (loss) income before reclassifications	(30,853)
Net current-period other comprehensive (loss) income	(30,853)
Currency translation adjustments \| Simon Property Group, L.P.
Changes in accumulated other comprehensive income (loss)
Beginning Balance	(135,940)
Other comprehensive (loss) income before reclassifications	(35,797)
Net current-period other comprehensive (loss) income	(35,797)
Ending balance	(171,737)
Accumulated derivative gains (losses), net
Changes in accumulated other comprehensive income (loss)
Other comprehensive (loss) income before reclassifications	17,645
Amounts reclassified from accumulated other comprehensive income (loss)	5,144
Net current-period other comprehensive (loss) income	22,789
Accumulated derivative gains (losses), net \| Simon Property Group, L.P.
Changes in accumulated other comprehensive income (loss)
Beginning Balance	9,263
Other comprehensive (loss) income before reclassifications	20,355
Amounts reclassified from accumulated other comprehensive income (loss)	5,929
Net current-period other comprehensive (loss) income	26,284
Ending balance	35,547
Net unrealized losses on marketable securities
Changes in accumulated other comprehensive income (loss)
Other comprehensive (loss) income before reclassifications	(76)
Net current-period other comprehensive (loss) income	(76)
Net unrealized losses on marketable securities \| Simon Property Group, L.P.
Changes in accumulated other comprehensive income (loss)
Beginning Balance	(425)
Other comprehensive (loss) income before reclassifications	(88)
Net current-period other comprehensive (loss) income	(88)
Ending balance	$ (513)

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