Intangible Assets and Liabilities - Components of intangible assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of finite lived intangible assets and liabilities
Intangible assets and liabilities, gross	$ 120.7	$ 116.0
Intangible assets and liabilities, accumulated amortization	$ 46.5	44.9
Assets and liabilities, weighted avg. life (years)	18 years 6 months
Below-market lease intangibles [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ (8.8)	(7.9)
Liabilities accumulated amortization	$ (3.2)	(3.7)
Liabilities, weighted avg. life (years)	38 years
Deferred financing costs [Member] | Other liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ 9.4	9.8
Liabilities accumulated amortization	$ 4.0	3.3
Liabilities, weighted avg. life (years)	6 years
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	5.4	7.3
Assets accumulated amortization	$ 0.5	5.1
Assets, weighted avg. life (years)	3 years 7 months 6 days
Above-market lease intangibles [Member] | Other assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 24.5	21.8
Assets accumulated amortization	$ 5.4	4.5
Assets, weighted avg. life (years)	54 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	$ 0.8	0.7
Assets, weighted avg. life (years)	26 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	$ 84.1	78.9
Assets accumulated amortization	$ 39.0	$ 35.0
Assets, weighted avg. life (years)	5 years 10 months 24 days