Intangible Assets and Liabilities - Components of intangible assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of finite lived intangible assets and liabilities
Intangible assets and liabilities, gross	$ 178.8	$ 148.3
Intangible assets and liabilities, accumulated amortization	$ 66.8	60.4
Assets and liabilities, weighted avg. life (years)	16 years 7 months 6 days
Below Market Lease Intangibles [Member] | Other Liabilities [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ (7.3)	(7.3)
Liabilities accumulated amortization	$ (4.0)	(4.0)
Liabilities, weighted avg. life (years)	6 years 8 months 12 days
Debt Issuance Costs [Member] | Notes and Bonds Payable [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 9.2	9.3
Assets accumulated amortization	$ 3.5	2.8
Assets, weighted avg. life (years)	5 years 9 months 18 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
Debt Issuance Costs [Member] | Other Assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	5.8	5.4
Assets accumulated amortization	$ 0.8	3.2
Assets, weighted avg. life (years)	3 years 9 months 18 days
Above-market Lease Intangibles (Lessor) [Member] | Other Assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 4.0	4.5
Assets accumulated amortization	$ 2.8	3.3
Assets, weighted avg. life (years)	3 years 10 months 24 days
Customer Relationship Intangibles (Lessor) [Member] | Other Assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 4.1	2.7
Assets accumulated amortization	$ 1.6	$ 1.0
Assets, weighted avg. life (years)	43 years 1 month 6 days
Below Market Lease Intangibles [Member]
Schedule of finite lived intangible assets and liabilities
Assets, weighted avg. life (years)		3 years 9 months 18 days
At Market Lease Intangibles [Member] | Real Estate Properties [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 147.9	$ 114.4
Assets accumulated amortization	$ 59.8	52.0
Assets, weighted avg. life (years)	5 years 4 months 24 days
Above- Market Lease Intangibles (Lessee) [Member] | Right-of-use Assets [Member]
Schedule of finite lived intangible assets and liabilities
Liabilities gross balance	$ (7.2)	(2.0)
Liabilities accumulated amortization	$ (0.2)	(0.1)
Liabilities, weighted avg. life (years)	75 years 6 months
Below-Market Lease Intangibles (Lessee) [Member]
Schedule of finite lived intangible assets and liabilities
Assets, weighted avg. life (years)	65 years 1 month 6 days
Below-Market Lease Intangibles (Lessee) [Member] | Right-of-use Assets [Member]
Schedule of finite lived intangible assets and liabilities
Assets gross balance	$ 18.8	17.8
Assets accumulated amortization	$ 2.5	$ 2.2
Assets, weighted avg. life (years)	63 years