Investments in Unconsolidated Companies (Summarized Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Rental revenue	$ 60,446	$ 71,424	$ 122,019
Equity Method Investment, Gain (Loss) on Sale of Properties	25,879	4,986	100,806
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	44,372	20,673	122,727
Equity in earnings (loss) of unconsolidated joint ventures	21,444	63,310	$ 47,403
Land, buildings and tenant improvements, net	328,959	383,581
Construction in progress	43,892	65,715
Undeveloped land	28,247	30,170
Other assets	88,448	76,695
Total assets	489,546	556,161
Indebtedness	209,584	235,497
Other liabilities	38,172	39,497
Total liabilities	247,756	274,994
Owners' equity	241,790	281,167
Total liabilities and equity	489,546	556,161
Investments in and advances to unconsolidated joint ventures	110,795	126,487
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 11,400	$ 6,400