Segment Reporting (Reportable Segments Consolidated Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Total Assets	$ 6,862,081	$ 6,895,515
Corporate, Non-Segment [Member]
Total Assets	485,689	569,136
Operating Segments [Member]
Total Assets	6,376,392	6,326,379
Operating Segments [Member] | Industrial [Member]
Total Assets	4,712,532	4,552,107
Operating Segments [Member] | Medical Office [Member]
Total Assets	1,319,955	1,269,546
Operating Segments [Member] | All Other Segments [Member]
Total Assets	214,130	367,469
Operating Segments [Member] | Service Operations [Member]
Total Assets	$ 129,775	$ 137,257