Other Assets - Schedule of Other Assets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Other Assets [Abstract]
Development project asset	$ 41.1	$ 55.3
Straight line rent	32.5	24.0
Goodwill	23.9	23.9
Hedge assets	21.2	2.4
Prepaid expenses	17.8	13.3
Leasing commissions, net of accumulated amortization of $3.3 and $2.2 at September 30, 2018 and December 31, 2017, respectively	11.8	10.1
Other, net of accumulated amortization of $2.7 and $2.6 at September 30, 2018 and December 31, 2017, respectively	11.3	10.7
Marketable securities	0.0	7.5
VAT receivable	4.4	5.0
Deposits	3.0	3.5
Other Assets	246.8	263.1
Accumulated amortization, leasing commissions	3.3	2.2
Accumulated amortization, other	2.7	2.6
Furniture and Fixtures [Member]
Other Assets [Abstract]
Furniture and equipment net of accumulated depreciation of $38.5 and $35.8 at September 30, 2018 and December 31, 2017, respectively	33.6	44.3
Accumulated amortization, office furniture and equipment	38.5	35.8
Above Market Leases [Member]
Other Assets [Abstract]
Above-market leases, net of accumulated amortization of $48.9 and $44.3 at September 30, 2018 and December 31, 2017, respectively	46.2	63.1
Accumulated amortization, above-market leases	$ 48.9	$ 44.3