Property (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Number of centers sold | property	15
Proceeds from sale and disposition of property	$ 464,100
Gain on sale of property	$ 189,914	$ 207,865	$ 218,611
Number of real estate properties acquired | property	5
Gross payments to acquire real estate	$ 219,600
Investment in new development projects	109,700
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Property, Plant and Equipment [Line Items]
Gain on sale of property	$ 189,800