Investments in Unconsolidated Companies (Summarized Financial Information) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity Method Investments and Joint Ventures [Abstract]
Rental revenue	$ 291,534	$ 272,937	$ 228,378
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	3,125	10,709	19,202
Land, buildings and tenant improvements, net	1,991,823	2,051,412
Construction in progress	61,663	12,208
Undeveloped land	175,143	177,742
Other assets	289,173	309,409
Total assets	2,517,802	2,550,771
Indebtedness	1,314,502	1,317,554
Other liabilities	70,519	71,241
Total liabilities	1,385,021	1,388,795
Owners' equity	1,132,781	1,161,976
Total liabilities and equity	$ 2,517,802	$ 2,550,771