Real Estate (Carrying Value of Properties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	$ 1,094,470	$ 1,184,927
Building and improvements	4,501,921	5,131,648
Accumulated Depreciation	940,115	1,148,928
Total Real Estate	5,596,391	6,316,575
Depreciation	166,800	181,000	$ 179,100
Industrial Property [Member]
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	919,951	824,140
Building and improvements	3,757,063	3,637,484
Accumulated Depreciation	734,595	698,456
Total Real Estate	4,677,014	4,461,624
Office Building [Member]
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	174,519	360,787
Building and improvements	744,858	1,494,164
Accumulated Depreciation	205,520	450,472
Total Real Estate	$ 919,377	$ 1,854,951