Other Assets - Schedule of Other Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Other Assets [Abstract]
Loan purchases and originations	$ 97.3	$ 37.5
Straight line rent receivable	56.7	47.3
Deferred taxes	26.1	24.4
Hedge assets	24.0	32.6
Goodwill	23.9	23.9
Other, net of accumulated amortization of $2.2 and $2.0 at September 30, 2020 and December 31, 2019, respectively	17.9	16.5
Prepaid expenses	15.1	14.3
Right of use asset, net	12.4	13.6
Leasing commissions, net of accumulated amortization of $6.4 and $4.7 at September 30, 2020 and December 31, 2019, respectively	12.4	11.9
Marketable Securities	8.8	0.0
Other Assets	334.8	271.8
Accumulated amortization, other	2.2	2.0
Accumulated amortization, leasing commissions	6.4	4.7
Above Market Leases [Member]
Other Assets [Abstract]
Above-market leases, net of accumulated amortization of $56.1 and $51.0 at September 30, 2020 and December 31, 2019, respectively	16.6	26.1
Accumulated amortization, above-market leases	56.1	51.0
Furniture and Fixtures [Member]
Other Assets [Abstract]
Furniture and equipment net of accumulated depreciation of $25.3 and $21.9 at September 30, 2020 and December 31, 2019, respectively	23.6	23.7
Accumulated amortization, office furniture and equipment	$ 25.3	$ 21.9