Subsequent Events (Narrative) (Details) $ in Thousands			12 Months Ended
	Feb. 19, 2016	Feb. 12, 2016 USD ($) center	Dec. 31, 2015 USD ($) property center	Dec. 31, 2014 USD ($) property
Subsequent Event [Line Items]
Number of real estate properties | property			2	2
Assets held by joint venture			$ 3,901,945	$ 3,805,915
Debt held by joint venture			$ 1,879,841
Number of centers sold | property			11
Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of voting interest acquired		49.00%
Proceeds from business acquisition		$ 2,500
Number of centers sold | center		1
Deferred compensation plan, period after common shares of beneficial interest have vested	6 months
Equity Method Investee [Member]
Subsequent Event [Line Items]
Number of centers sold | property				4
Equity Method Investee [Member] | 51% Owned Real Estate Joint Venture [Member]
Subsequent Event [Line Items]
Equity interest in joint venture (percent)			51.00%
Number of real estate properties | center			3
Assets held by joint venture			$ 43,700
Debt held by joint venture			$ 72,400