Investments in Unconsolidated Companies (Summarized Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]
Rental revenue	$ 160,543	$ 230,093	$ 240,064
Equity Method Investment, Gain (Loss) on Sale of Properties	23,696	121,713	121,404
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	60,772	143,857	116,832
Income (Loss) from Equity Method Investments	(3,304)	94,317	$ 54,116
Land, buildings and tenant improvements, net	1,029,803	1,251,470
Construction in progress	64,646	34,680
Undeveloped land	115,773	115,252
Other assets	144,337	168,653
Total assets	1,354,559	1,570,055
Indebtedness	413,651	639,810
Other liabilities	91,836	71,818
Total liabilities	505,487	711,628
Owners' equity	849,072	858,427
Total liabilities and equity	1,354,559	1,570,055
Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures	268,390	293,650
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 33,700	$ 1,000