Investments in Real Estate - Schedule of Acquisitions (Details) £ in Millions, ft² in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 GBP (£) ft² state property	Dec. 31, 2019 USD ($) ft² state property	Dec. 31, 2018 USD ($) ft² state property
Real Estate [Line Items]
Number of properties | property	789	789	764
Square feet (sq ft) | ft²	13.7	13.7	5.2
Investment | $		$ 3,715.2	$ 1,797.5
Weighted average lease term (years)	13 years 6 months	13 years 6 months	14 years 9 months 18 days
Initial average cash lease yield (percent)	6.40%	6.40%	6.40%
New properties
Real Estate [Line Items]
Number of properties, new | property	771	771
Square feet (sq ft) | ft²	13.2	13.2
Investment | $		$ 3,658.6
Weighted average lease term (years)	13 years 4 months 24 days	13 years 4 months 24 days
Initial average cash lease yield (percent)	6.40%	6.40%
New properties | U.S.
Real Estate [Line Items]
Number of properties, new | property	753	753	750
Number of states | state	45	45	39
Square feet (sq ft) | ft²	11.6	11.6	4.1
Investment | $		$ 2,860.8	$ 1,717.2
Weighted average lease term (years)	13 years	13 years	14 years 10 months 24 days
Initial average cash lease yield (percent)	6.80%	6.80%	6.30%
New properties | U.K.
Real Estate [Line Items]
Number of properties, new | property	18	18
Square feet (sq ft) | ft²	1.6	1.6
Investment	£ 625.8	$ 797.8
Weighted average lease term (years)	15 years 7 months 6 days	15 years 7 months 6 days
Initial average cash lease yield (percent)	5.20%	5.20%
Properties under development | U.S.
Real Estate [Line Items]
Number of properties, under development | property	18	18	14
Square feet (sq ft) | ft²	0.5	0.5	1.1
Investment | $		$ 56.6	$ 80.3
Weighted average lease term (years)	15 years 1 month 6 days	15 years 1 month 6 days	12 years 3 months 18 days
Initial average cash lease yield (percent)	7.30%	7.30%	6.90%