Discontinued Operations and Assets Held for Sale (Table Illustration of Number of Properties in Discontinued Operations) (Details) - buildings	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	81	0
Total number of properties in discontinued operations	81
Continuing Operations, Number of In-service Properties Held for Sale	0
Continuing Operations, Number of Real Estate Properties Sold	15	17	32
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale	64
Number of Real Estate Properties Held for Sale	0
Number of Real Estate Properties Sold	15	98	32
Total Properties Sold or Classified as Held for Sale	145
Industrial [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	0	0
Total number of properties in discontinued operations	0
Non-reportable segments
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	81	0
Total number of properties in discontinued operations	81
Medical Office Portfolio Sale [Member]
Continuing Operations, Number of Real Estate Properties Sold		4
Number of Real Estate Properties Sold		85