Segment Reporting (Reportable Segments Consolidated Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Total Assets	$ 6,917,113	$ 7,754,839
Operating Segments [Member]
Total Assets	6,326,379	7,389,809
Operating Segments [Member] | Industrial [Member]
Total Assets	4,552,107	4,677,047
Operating Segments [Member] | Medical Office [Member]
Total Assets	1,269,546	1,229,632
Operating Segments [Member] | Office Building [Member]
Total Assets	367,469	1,252,627
Operating Segments [Member] | All Other Segments [Member]
Total Assets	0	71,741
Operating Segments [Member] | Service Operations [Member]
Total Assets	137,257	158,762
Corporate, Non-Segment [Member]
Total Assets	$ 590,734	$ 365,030