Intangibles Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Finite-Lived Intangibles
Finite-lived intangible assets, gross	$ 441,807	$ 408,858
Accumulated amortization	(143,160)	(125,924)
Assets Total	298,647	282,934
Finite-lived intangible liabilities, gross	17,375	16,650
Accumulated amortization	(6,113)	(5,341)
Liabilities Total	11,262	11,309
Below Market Leases
Finite-Lived Intangibles
Finite-lived intangible liabilities, gross	13,548	12,823
Liabilities, Weighted average remaining amortization period in years	13 years	13 years 8 months 12 days
Above Market Leasehold Interests
Finite-Lived Intangibles
Finite-lived intangible liabilities, gross	3,827	3,827
Liabilities, Weighted average remaining amortization period in years	33 years 3 months 18 days	34 years
In Place Leases
Finite-Lived Intangibles
Finite-lived intangible assets, gross	197,185	174,615
Assets, Weighted average remaining amortization period in years	8 years 8 months 12 days	9 years 8 months 12 days
Tenant Relationships
Finite-Lived Intangibles
Finite-lived intangible assets, gross	189,616	178,269
Assets, Weighted average remaining amortization period in years	10 years 7 months 6 days	11 years 7 months 6 days
Above Market Leases
Finite-Lived Intangibles
Finite-lived intangible assets, gross	25,878	25,387
Assets, Weighted average remaining amortization period in years	6 years 3 months 18 days	6 years 10 months 24 days
Below Market Leasehold Interests
Finite-Lived Intangibles
Finite-lived intangible assets, gross	$ 29,128	$ 30,587
Assets, Weighted average remaining amortization period in years	63 years 10 months 24 days	69 years 4 months 24 days