Intangible Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Amortizable Intangible Assets [Member]
Lease intangibles:
Less: accumulated depreciation	$ (46,921)	$ (24,666)
Finite-lived intangible assets, net	411,805	334,137
Amortizable Intangible Liabilities [Member]
Lease intangibles:
Less: accumulated depreciation	2,880	1,187
Finite-lived intangible assets, net	(45,089)	(25,622)
In-place lease | Amortizable Intangible Assets [Member]
Lease intangibles:
Finite-lived intangible assets, gross	373,489	286,913
Tenant relationship | Amortizable Intangible Assets [Member]
Lease intangibles:
Finite-lived intangible assets, gross	13,079	13,102
Above-market rent | Amortizable Intangible Assets [Member]
Lease intangibles:
Finite-lived intangible assets, gross	72,158	58,788
Below-market rent | Amortizable Intangible Liabilities [Member]
Lease intangibles:
Finite-lived intangible assets, gross	$ (47,969)	$ (26,809)