Discontinued Operations and Assets Held for Sale (Table Illustration of Number of Properties in Discontinued Operations) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2015 buildings	Dec. 31, 2014 buildings
Number of properties held for sale in discontinued operations	61
Number of properties sold in discontinued operations	1	12
Total number of properties in discontinued operations	74
Continuing Operations, Number of In-service Properties Held for Sale	52
Continuing Operations, Number of Real Estate Properties Sold	11	17
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale	80
Number of Real Estate Properties Held for Sale	113
Number of Real Estate Properties Sold	12	29
Total Properties Sold or Classified as Held for Sale	154
Industrial [Member]
Number of properties held for sale in discontinued operations	5
Number of properties sold in discontinued operations	0	11
Total number of properties in discontinued operations	16
Office [Member]
Number of properties held for sale in discontinued operations	56
Number of properties sold in discontinued operations	0	0
Total number of properties in discontinued operations	56
Medical Office [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	1	1
Total number of properties in discontinued operations	2