Discontinued Operations and Assets Held for Sale (Table Illustration of Number of Properties in Discontinued Operations) (Details) - buildings	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	62	12	25
Total number of properties in discontinued operations	99
Continuing Operations, Number of In-service Properties Held for Sale	4
Continuing Operations, Number of Real Estate Properties Sold	91	17	13
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale	125
Number of Real Estate Properties Held for Sale	4
Number of Real Estate Properties Sold	153	29	38
Total Properties Sold or Classified as Held for Sale	224
Office Building [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	56	0	12
Total number of properties in discontinued operations	68
Industrial [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	5	11	6
Total number of properties in discontinued operations	22
Medical Office [Member]
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	1	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	0	1
Total number of properties in discontinued operations	1