Investments in Unconsolidated Entities - Unconsolidated Entity Transactions (Details) $ in Thousands		3 Months Ended
	Sep. 30, 2015 property	Mar. 31, 2018 USD ($) property	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investment in Unconsolidated Entities
Share of net income, net of amortization of our excess investment		$ 90,026	$ 69,085
HBS
Investment in Unconsolidated Entities
Ownership interest (as a percent)		11.70%		11.70%
Number of properties contributed to form joint venture | property		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
Contribution to form joint venture		178,500
Share of net income, net of amortization of our excess investment		4,000	3,200
Total revenues		87,200	81,900
Total operating income		76,800	64,900
Consolidated net income		$ 51,600	$ 44,100