Property (Narrative) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Number of centers sold | property	12
Proceeds from sale and disposition of property	$ 375,100
Gain on sale of property	$ 143,963	$ 173,077
Number of real estate properties | property	2
Acquisition of real estate property	$ 55,100
Investment in new development	81,800
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of property	$ 144,000