Investments in Unconsolidated Entities and International Investments - Unconsolidated Entity Transactions (Details) $ / shares in Units, $ in Thousands					3 Months Ended				9 Months Ended		12 Months Ended	17 Months Ended	29 Months Ended
	Oct. 16, 2019 USD ($)	Sep. 25, 2018 $ / shares shares	Jun. 07, 2018 USD ($)	Sep. 15, 2016 item	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 19, 2019	May 31, 2017
Investment in Unconsolidated Entities
Gain upon acquisition of controlling interests, sale or disposal of, or recovery on, assets and interests in unconsolidated entities and impairment, net					$ 10,141				$ 12,822	$ 144,949
Insurance proceeds recorded as business interruption									3,787	16,160
Gain on interest in unconsolidated entities										35,621
Share of net income, net of amortization of our excess investment					119,706		$ 134,408		316,691	325,263
Hotel
Investment in Unconsolidated Entities
Ownership interests acquired (as a percent)														50.00%
Ownership interest after acquisition (as a percent)														100.00%
Outlets at Orange
Investment in Unconsolidated Entities
Ownership interests acquired (as a percent)		50.00%
Ownership interest after acquisition (as a percent)		100.00%
Simon Property Group, L.P.
Investment in Unconsolidated Entities
Gain upon acquisition of controlling interests, sale or disposal of, or recovery on, assets and interests in unconsolidated entities and impairment, net					10,141				12,822	144,949
Insurance proceeds recorded as business interruption									3,787	16,160
Gain on interest in unconsolidated entities										35,621
Share of net income, net of amortization of our excess investment					$ 119,706		134,408		$ 316,691	325,263
Simon Property Group, L.P. | Outlets at Orange
Investment in Unconsolidated Entities
Number of units issued in connection with acquisition of the remaining interest in orange outlet | shares		475,183
Business acquisition price (in dollars per share) | $ / shares		$ 176.99
Colorado Mills
Investment in Unconsolidated Entities
Impairment charges								$ 32,500
Insurance proceeds recorded as business interruption												$ 58,300	$ 66,800
Gain on business interruption											$ 25,800
Aventura Mall
Investment in Unconsolidated Entities
Loan defeasance charge			$ 30,900
Write off of deferred debt issuance cost			6,500
Mortgages | Aventura Mall
Investment in Unconsolidated Entities
Debt refinanced			1,200,000
Construction loan | Aventura Mall
Investment in Unconsolidated Entities
Debt refinanced			200,800
4.12% fixed interest rate mortgage maturing July 2028 | Aventura Mall
Investment in Unconsolidated Entities
Debt issued			$ 1,750,000
Fixed interest rate (as a percent)			4.12%
Aventura Mall
Investment in Unconsolidated Entities
Ownership interest (as a percent)			33.30%
Share of early debt repayment charge			$ 12,500
Colorado Mills
Investment in Unconsolidated Entities
Ownership interest (as a percent)															37.50%
Gain upon acquisition of controlling interests, sale or disposal of, or recovery on, assets and interests in unconsolidated entities and impairment, net										9,700
Aeropostale
Investment in Unconsolidated Entities
Number of joint ventures | item				2
Aeropostale Retail Operations
Investment in Unconsolidated Entities
Ownership interest (as a percent)					44.95%				44.95%				44.95%
Authentic Brands Group LLC
Investment in Unconsolidated Entities
Ownership interest (as a percent)					5.40%				5.40%				5.40%
Gain on interest in unconsolidated entities									$ 35,600
HBS
Investment in Unconsolidated Entities
Ownership interest (as a percent)					11.70%				11.70%		11.70%		11.70%
Share of net income, net of amortization of our excess investment					$ (5,200)		$ 4,300		$ (13,300)	11,900
Total revenues									100,200	258,800
Total operating income									13,800	162,200
Consolidated net income									$ (23,900)	$ 90,600
Shop Premium Outlets
Investment in Unconsolidated Entities
Ownership interest (as a percent)	45.00%
Contribution to form joint venture	$ 276,800
Unconsolidated properties | Disposed by Sales | Residential properties
Investment in Unconsolidated Entities
Proceeds from sale or disposal of real estate assets						$ 17,300
Gain (loss) on disposition of interest in properties						$ 15,600