Investments in Real Estate - Schedule of Acquisitions Narrative (Details) £ in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) property_investment industry	Sep. 30, 2020 GBP (£) property_investment industry	Sep. 30, 2019 USD ($) property_investment industry	Sep. 30, 2019 GBP (£) property_investment industry
Real Estate [Line Items]
Number of investments in properties that caused any tenant to be 10% of more of total assets | property_investment	0	0	0	0
Value of properties acquired during the period	$ 1,298.9		$ 2,025.7
Rental revenue generated from acquisitions from investment grade tenants (as a percent)	56.00%	56.00%	25.00%	25.00%
New and under development
Real Estate [Line Items]
Acquired properties, percentage leased at the acquisition date (as a percent)	100.00%	100.00%	100.00%	100.00%
New properties
Real Estate [Line Items]
Value of properties acquired during the period	$ 1,275.6		$ 1,989.7
Number of industries in which tenants operate | industry	23	23	19	19
New properties | Retail
Real Estate [Line Items]
Property type acquired based on rental revenue (as a percent)	96.90%	96.90%	89.60%	89.60%
New properties | Industrial
Real Estate [Line Items]
Property type acquired based on rental revenue (as a percent)	3.10%	3.10%	10.40%	10.40%
New properties | U.K.
Real Estate [Line Items]
Value of properties acquired during the period	$ 453.7	£ 356.7	$ 576.8	£ 456.1