Schedule III - Real Estate and Accumulated Depreciation (Details 1) (USD $) In Thousands, unless otherwise specified					12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013 Real Estate [Member]		Dec. 31, 2012 Real Estate [Member]	Dec. 31, 2011 Real Estate [Member]	Dec. 31, 2013 Corporate Property [Member]		Dec. 31, 2012 Corporate Property [Member]	Dec. 31, 2011 Corporate Property [Member]	Dec. 31, 2013 Land held for development [Member]	Dec. 31, 2012 Land held for development [Member]	Dec. 31, 2011 Land held for development [Member]	Dec. 31, 2013 Construction in Progress [Member]	Dec. 31, 2012 Construction in Progress [Member]	Dec. 31, 2011 Construction in Progress [Member]	Dec. 31, 2013 Disposal of previously consolidated VIE [Member]	Dec. 31, 2012 Disposal of previously consolidated VIE [Member]	Dec. 31, 2011 Disposal of previously consolidated VIE [Member]
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Beginning Balance, Total Property	$ 3,084,166	$ 2,830,931	$ 2,831,732	$ 2,605,516
Additions during the period:
Total Property					372,946		160,082	186,923	62		27	101	0	0	4,403	0	5,608	101,282
Retirement/dispositions:
Total Property					(111,656)		(128,104)	(65,680)	0		(221)	(813)	(8,117)	0	0				0	(38,193)	0
Ending Balance, Total Property	3,084,166	2,830,931	2,831,732	2,605,516	3,061,715	[1],[2]			5,397	[1],[2]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Beginning Balance, Accumulated Depreciation	642,320	586,920	536,682	500,406
Additions during the period:
Accumulated Depreciation					98,090		95,110	85,325	211		219	243	26	26	26	0	0	0
Retirement/dispositions:
Accumulated Depreciation					(42,927)		(44,896)	(48,505)	0		(221)	(813)	0	0	0				0	0	0
Ending Balance, Accumulated Depreciation	$ 642,320	$ 586,920	$ 536,682	$ 500,406	$ 638,728	[1],[3]			$ 3,503	[1],[3]

[1] Depreciation is provided for on a straight-line basis on buildings and improvements over 3.3 to 39.0 years, lease intangibles over 2.0 to 93.1 years, personal property over 1.9 to 15.8 years, and land improvements over 15.0 to 38.1 years.

[2] Total assets as of December 31, 2013 have an estimated aggregate total cost of $3.1 billion for federal income tax purposes.

[3] Includes three assets held for sale as of December 31, 2013 of approximately $17.0 million (gross) and accumulated depreciation of $10.2 million, one asset held for sale as of December 31, 2012 of approximately $9.6 million (gross) and accumulated depreciation of $6.3 million; and 15 assets held for sale as of December 31, 2011 of $52.8 million (gross) and accumulated depreciation of $24.6 million.