Investments in Unconsolidated Companies (Summarized Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Rental revenue	$ 122,019	$ 160,543	$ 230,093
Equity Method Investment, Gain (Loss) on Sale of Properties	100,806	23,696	121,713
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	122,727	60,772	143,857
Income (Loss) from Equity Method Investments	47,403	(3,304)	$ 94,317
Land, buildings and tenant improvements, net	529,926	1,029,803
Construction in progress	31,838	64,646
Undeveloped land	90,560	115,773
Other assets	91,045	144,337
Total assets	743,369	1,354,559
Indebtedness	172,811	413,651
Other liabilities	32,633	91,836
Total liabilities	205,444	505,487
Owners' equity	537,925	849,072
Total liabilities and equity	743,369	1,354,559
Investments in and advances to unconsolidated companies	197,807	268,390
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 22,200	$ 33,700