Investments in Unconsolidated Companies (Summarized Financial Information) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Method Investments and Joint Ventures [Abstract]
Rental revenue	$ 230,093,000	$ 240,064,000	$ 291,534,000
Equity Method Investment, Gain (Loss) on Sale of Properties	121,713,000	121,404,000	6,792,000
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	143,857,000	116,832,000	3,125,000
Income (Loss) from Equity Method Investments	94,317,000	54,116,000	4,674,000
Land, buildings and tenant improvements, net	1,251,470,000	1,656,231,000
Construction in progress	34,680,000	12,338,000
Undeveloped land	115,252,000	126,556,000
Other assets	168,653,000	206,414,000
Total assets	1,570,055,000	2,001,539,000
Indebtedness	639,810,000	890,513,000
Other liabilities	71,818,000	93,291,000
Total liabilities	711,628,000	983,804,000
Owners' equity	858,427,000	1,017,735,000
Total liabilities and equity	1,570,055,000	2,001,539,000
Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures	293,650,000	342,947,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 1,000,000	$ 4,200,000