Intangible Assets and Liabilities - Components of intangible assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Schedule of finite lived intangible assets and liabilities
Intangible assets and liabilities, gross	$ 116.0	$ 112.6
Intangible assets and liabilities, accumulated amortization	$ 44.9	40.8
Assets and liabilities, weighted avg. life (years)	17 years 9 months 18 days
Below-market lease intangibles [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ (7.9)	(7.6)
Liabilities accumulated amortization	$ (3.7)	(3.0)
Liabilities, weighted avg. life (years)	13 years 10 months 24 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	0.0
Deferred financing costs [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	17.1	17.6
Assets accumulated amortization	$ 8.4	7.7
Assets, weighted avg. life (years)	5 years 4 months 24 days
Above-market lease intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 21.8	20.9
Assets accumulated amortization	$ 4.5	3.6
Assets, weighted avg. life (years)	53 years 9 months 18 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	$ 0.7	0.7
Assets, weighted avg. life (years)	27 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	$ 78.9	75.6
Assets accumulated amortization	$ 35.0	$ 31.8
Assets, weighted avg. life (years)	6 years 4 months 24 days