Summary of Significant Accounting Policies - AOCI, Simon Property Group, Inc. (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Changes in accumulated other comprehensive income (loss)
Beginning balance	$ 3,686,168
Ending balance	3,383,616
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss)
Beginning balance	(110,453)
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)
Ending balance	(118,593)
Currency translation adjustments
Changes in accumulated other comprehensive income (loss)
Beginning balance	(118,138)
Other comprehensive (loss) income before reclassifications	(30,853)
Net current-period other comprehensive (loss) income	(30,853)
Ending balance	(148,991)
Accumulated derivative gains (losses), net
Changes in accumulated other comprehensive income (loss)
Beginning balance	8,055
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
Ending balance	30,844
Net unrealized losses on marketable securities
Changes in accumulated other comprehensive income (loss)
Beginning balance	(370)
Other comprehensive (loss) income before reclassifications	(76)
Net current-period other comprehensive (loss) income	(76)
Ending balance	$ (446)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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