Investments in Real Estate - Schedule of Acquisitions (Details) £ in Millions, ft² in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020 GBP (£) ft² state property	Mar. 31, 2020 USD ($) ft² state property	Mar. 31, 2019 USD ($) ft² property	Dec. 31, 2019
Real Estate [Line Items]
Number of properties | property	65	65	105
Square feet (sq ft) | ft²	2.0	2.0	2.3
Investment | $		$ 486.0	$ 519.5
Weighted average lease term (years)	14 years 1 month 6 days	14 years 1 month 6 days		17 years
Initial average cash lease yield (percent)	6.00%	6.00%	6.70%
New properties
Real Estate [Line Items]
Number of properties, new | property	58	58
Square feet (sq ft) | ft²	1.8	1.8
Investment | $		$ 483.9
Weighted average lease term (years)	14 years 2 months 12 days	14 years 2 months 12 days
Initial average cash lease yield (percent)	6.00%	6.00%
New properties | U.S.
Real Estate [Line Items]
Number of properties, new | property	54	54	97
Number of states	22	22	25
Square feet (sq ft) | ft²	1.4	1.4	1.9
Investment | $		$ 318.3	$ 508.6
Weighted average lease term (years)	14 years 9 months 18 days	14 years 9 months 18 days		17 years
Initial average cash lease yield (percent)	6.50%	6.50%	6.70%
New properties | U.K.
Real Estate [Line Items]
Number of properties, new | property	4	4
Square feet (sq ft) | ft²	0.4	0.4
Investment	£ 133.3	$ 165.6
Weighted average lease term (years)	12 years 6 months	12 years 6 months
Initial average cash lease yield (percent)	5.10%	5.10%
Properties under development | U.S.
Real Estate [Line Items]
Number of properties, under development | property	7	7	8
Square feet (sq ft) | ft²	0.2	0.2	0.4
Investment | $		$ 2.1	$ 10.9
Weighted average lease term (years)	10 years 7 months 6 days	10 years 7 months 6 days		17 years 3 months 18 days
Initial average cash lease yield (percent)	7.50%	7.50%	7.20%