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, 2014 buildings	Dec. 31, 2013 buildings
Number of properties held for sale in discontinued operations	3
Number of properties sold in discontinued operations	10	25
Total number of properties in discontinued operations	38
Continuing Operations, Number of In-service Properties Held for Sale	0
Continuing Operations, Number of Real Estate Properties Sold	1	13
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale	14
Number of Real Estate Properties Held for Sale	3
Number of Real Estate Properties Sold	11	38
Total Properties Sold or Classified as Held for Sale	52
Industrial [Member]
Number of properties held for sale in discontinued operations	2
Number of properties sold in discontinued operations	9	6
Total number of properties in discontinued operations	17
Office [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	12
Total number of properties in discontinued operations	12
Medical Office [Member]
Number of properties held for sale in discontinued operations	1
Number of properties sold in discontinued operations	1	6
Total number of properties in discontinued operations	8
Retail [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	1
Total number of properties in discontinued operations	1