Intangible Assets Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Intangible Assets [Line Items]
Total Cost	$ 142,738	$ 152,611
Accumulated Amortization	(76,634)	(81,991)
Intangible Assets, net	66,104	70,620
In-place lease value
Intangible Assets [Line Items]
Total Cost	83,905	87,909
Accumulated Amortization	(41,743)	(42,894)
Intangible Assets, net	42,162	45,015
Tenant relationship value
Intangible Assets [Line Items]
Total Cost	50,268	56,137
Accumulated Amortization	(33,019)	(37,389)
Intangible Assets, net	17,249	18,748
Above market leases acquired
Intangible Assets [Line Items]
Total Cost	8,565	8,565
Accumulated Amortization	(1,872)	(1,708)
Intangible Assets, net	6,693	6,857
Below market leases acquired
Intangible Assets [Line Items]
Total Cost	76,892	77,083
Accumulated Amortization	(44,990)	(43,224)
Intangible Assets, net	$ 31,902	$ 33,859