Segment Reporting (Reportable Segments Consolidated Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Total Assets	$ 6,896,960	$ 6,895,515
Corporate, Non-Segment [Member]
Total Assets	545,911	569,136
Operating Segments [Member]
Total Assets	6,351,049	6,326,379
Operating Segments [Member] | Industrial [Member]
Total Assets	4,614,478	4,552,107
Operating Segments [Member] | Medical Office [Member]
Total Assets	1,279,562	1,269,546
Operating Segments [Member] | All Other Segments [Member]
Total Assets	321,451	367,469
Operating Segments [Member] | Service Operations [Member]
Total Assets	$ 135,558	$ 137,257