Variable Interest Entities (Narrative) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) property joint_venture	Dec. 31, 2018 USD ($)	Dec. 31, 2017 property joint_venture
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures guaranteed by company	1		1
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures	9		9
Number of real estate properties | property	22		22
Variable interest entity, consolidated, additional contributions made | $	$ 100,000
Unconsolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Number of VIE real estate joint ventures	2		2
Number of joint venture arrangements	1
Variable interest entity, nonconsolidated, additional future funding | $	$ 79,000,000
Scenario, Forecast [Member] | Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Variable interest entity, consolidated, additional contributions made | $		$ 0