Variable Interest Entities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) property center joint_venture	Dec. 31, 2016 USD ($) property center joint_venture
Variable Interest Entity [Line Items]
Number of real estate properties | center		2	2
Number of VIE's guaranteed by company | joint_venture		1
Carrying amount, property, net		$ 207,969	$ 476,117
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures | joint_venture		9	9
Number of real estate properties | property		22	25
Carrying amount, property, net			$ 249,500
Additional contributions		$ 100	$ 2,500
Unconsolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures | joint_venture		2	2
Number of joint venture arrangements | joint_venture		1
Future additional equity and debt contributions		$ 93,000
Scenario, Forecast [Member] | Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Additional contributions	$ 100