Leases - Future Minimum Lease Rents (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 monthly_payment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Future Minimum Lease Rents Due [Abstract]
Asset Cost of Leased Property		$ 89.0	$ 90.1
Carrying Amount on Leased Property		62.7	64.5
Contingent Rent Expense on Leases		3.3	2.8	$ 2.8
Minimum Rent Expense on Leases		80.9	$ 75.9	$ 75.4
Direct Financing Lease, 2016		17.6
Direct Financing Lease, 2017		17.7
Direct Financing Lease, 2018		17.4
Direct Financing Lease, 2019		16.3
Direct Financing Lease, 2020		14.9
Thereafter		25.0
Total minimum rents receivable		108.9
Operating Lease, 2016		100.7
Operating Lease, 2017		100.7
Operating Lease, 2018		100.2
Operating Lease, 2019		98.4
Operating Lease, 2020		98.6
Thereafter		496.6
Total minimum rents receivable		$ 995.2
Forecast
Lease [Line Items]
Number of Monthly Obligation Payments in Fiscal Year | monthly_payment	11