Discontinued Operations and Assets Held for Sale (Table Illustration of Number of Properties in Discontinued Operations) (Details) - buildings	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of properties held for sale in discontinued operations		0
Number of properties sold in discontinued operations		81	0	62
Total number of properties in discontinued operations		143
Continuing Operations, Number of In-service Properties Held for Sale		1
Continuing Operations, Number of Real Estate Properties Sold		17	32	91
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale		141
Number of Real Estate Properties Held for Sale		1
Number of Real Estate Properties Sold		98	32	153
Total Properties Sold or Classified as Held for Sale		284
Industrial [Member]
Number of properties held for sale in discontinued operations		0
Number of properties sold in discontinued operations		0	0	5
Total number of properties in discontinued operations		5
Non-reportable segments
Number of properties held for sale in discontinued operations		0
Number of properties sold in discontinued operations		81	0	57
Total number of properties in discontinued operations		138
Medical Office Portfolio Sale [Member]
Continuing Operations, Number of Real Estate Properties Sold		4
Number of Real Estate Properties Sold	1	85