Real Estate Assets, Discontinued Operations and Assets Held for Sale (Table Illustration of Number of Properties in Discontinued Operations) (Details) - buildings	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Number of properties held for sale in discontinued operations	0
Number of properties sold in discontinued operations	0	0
Total number of properties in discontinued operations	0
Continuing Operations, Number of In-service Properties Held for Sale	0
Continuing Operations, Number of Real Estate Properties Sold	0	15
Continuing Operations, Number of Real Estate Properties Sold or Classified as Held for Sale	15
Number of Real Estate Properties Held for Sale	0
Number of Real Estate Properties Sold	0	15
Total Properties Sold or Classified as Held for Sale	15