Intangible Assets (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Intangible assets
Total Cost	$ 199,728	$ 222,160
Accumulated Amortization	(118,166)	(124,698)
Intangible assets, net	81,562	97,462
Below market leases acquired	37,940	29,233
Customer Relationships [Member]
Intangible assets
Total Cost	79,110	95,385
Accumulated Amortization	(47,036)	(52,113)
Intangible assets, net	32,074	43,272
Leases, Acquired-in-Place [Member]
Intangible assets
Total Cost	104,581	108,456
Accumulated Amortization	(62,542)	(63,010)
Intangible assets, net	42,039	45,446
Above market tenant leases acquired [Member]
Intangible assets
Total Cost	16,037	18,319
Accumulated Amortization	(8,588)	(9,575)
Intangible assets, net	7,449	8,744
Below market ground lease acquired [Member]
Intangible assets
Total Cost	79,966	67,198
Accumulated Amortization	(42,026)	(37,965)
Below market leases acquired	$ 37,940	$ 29,233