Property (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) property	Mar. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Number of centers sold | property	3
Proceeds from sale and disposition of property	$ 67,200
Gain on sale of property	$ 17,787	$ 109,045
Number of real estate properties | property	1
Acquisition of real estate property	$ 20,300
Investment in new development	22,500
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of property	$ 17,800