Intangible Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule of finite lived intangible assets and liabilities
Intangible assets and liabilities, gross	$ 98.1	$ 94.9
Intangible assets and liabilities, accumulated amortization	32.4	21.3
Assets and liabilities, weighted avg. life (years)	16 years 1 month 6 days
Below-market lease intangibles [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	(6.8)	(6.9)
Liabilities accumulated amortization	(1.9)	(1.4)
Liabilities, weighted avg. life (years)	14 years 7 months 6 days
Goodwill [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	3.5	3.5
Assets accumulated amortization	0	0
Deferred financing costs [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	17.6	17.6
Assets accumulated amortization	7.0	3.8
Assets, weighted avg. life (years)	4 years 3 months 18 days
Above-market lease intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	14.8	14.8
Assets accumulated amortization	2.1	1.5
Assets, weighted avg. life (years)	57 years 7 months 6 days
Customer relationship intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	2.6	2.6
Assets accumulated amortization	0.6	0.5
Assets, weighted avg. life (years)	30 years 7 months 6 days
At-market lease intangibles [Member] | Real estate properties [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	66.4	63.3
Assets accumulated amortization	$ 24.6	$ 16.9
Assets, weighted avg. life (years)	7 years