Investments in Real Estate - Schedule of Acquisitions Narrative (Details) £ in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) industry property_investment	Jun. 30, 2020 GBP (£) industry property_investment	Jun. 30, 2019 USD ($) industry property_investment	Jun. 30, 2019 GBP (£) industry property_investment
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	$ 640.2		$ 1,614.2
Rental revenue generated from acquisitions from investment grade tenants (as a percent)	37.00%	37.00%	18.00%	18.00%
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	$ 636.3		$ 1,590.1
Number of industries in which tenants operate | industry	17	17	17	17
New properties | Retail
Real Estate [Line Items]
Property type acquired based on rental revenue (as a percent)	96.50%	96.50%	99.10%	99.10%
New properties | Industrial
Real Estate [Line Items]
Property type acquired based on rental revenue (as a percent)	3.50%	3.50%	0.90%	0.90%
New properties | U.K.
Real Estate [Line Items]
Value of properties acquired during the period	$ 223.7	£ 180.1	$ 549.2	£ 433.9