Investments in Unconsolidated Entities - Unconsolidated Entity Transactions (Details) $ in Thousands				1 Months Ended	3 Months Ended			6 Months Ended
	Jun. 07, 2018 USD ($)	Sep. 15, 2016 item	Sep. 30, 2015 property	Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) property	Jun. 30, 2017 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2018 USD ($) property	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	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					$ 9,672	$ 4,989		$ 144,949	$ 4,989
Gain on interest in unconsolidated entities								35,621
Share of net income, net of amortization of our excess investment					$ 100,828	92,017		190,854	161,101
Colorado Mills
Investment in Unconsolidated Entities
Impairment charges						32,500
Proceeds of damaged properties								58,300
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%
HBS
Investment in Unconsolidated Entities
Ownership interest (as a percent)					11.70%			11.70%		11.70%
Number of properties contributed to form joint venture | property					42			42
Number of Kaufhof properties purchased by the joint venture | property			41
Committed amount to contribute								$ 100,000
Contributions for improvements to properties					$ 68,300			68,300		$ 68,300
Contribution to form joint venture							$ 178,500
Share of net income, net of amortization of our excess investment					$ 3,700	$ 3,300		7,600	6,500
Total revenues								174,200	183,000
Total operating income								102,300	177,900
Consolidated net income								$ 53,800	$ 129,700
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%
Authentic Brands Group LLC
Investment in Unconsolidated Entities
Ownership interest (as a percent)					5.78%			5.78%
Gain on interest in unconsolidated entities				$ 35,600
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
Aventura Mall
Investment in Unconsolidated Entities
Ownership interest (as a percent)	33.30%
Share of early debt repayment charge	$ 12,500