Summary of Significant Accounting Policies - AOCI, Simon Property Group, Inc. (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Changes in accumulated other comprehensive income (loss)
Beginning balance	$ 3,686,168
Ending balance	3,296,681
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss)
Beginning balance	(110,453)
Other comprehensive (loss) income before reclassifications	(21,661)
Amounts reclassified from accumulated other comprehensive income (loss)	6,097
Net current-period other comprehensive (loss) income	(15,564)
Ending balance	(126,017)
Currency translation adjustments
Changes in accumulated other comprehensive income (loss)
Beginning balance	(118,138)
Other comprehensive (loss) income before reclassifications	(40,766)
Net current-period other comprehensive (loss) income	(40,766)
Ending balance	(158,904)
Accumulated derivative gains (losses), net
Changes in accumulated other comprehensive income (loss)
Beginning balance	8,055
Other comprehensive (loss) income before reclassifications	18,781
Amounts reclassified from accumulated other comprehensive income (loss)	6,097
Net current-period other comprehensive (loss) income	24,878
Ending balance	32,933
Net unrealized losses on marketable securities
Changes in accumulated other comprehensive income (loss)
Beginning balance	(370)
Other comprehensive (loss) income before reclassifications	324
Net current-period other comprehensive (loss) income	324
Ending balance	$ (46)

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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