Investments in Real Estate - Schedule of Acquisitions (Details) $ in Thousands, £ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) ft² property state	Dec. 31, 2020 GBP (£) ft² property state	Dec. 31, 2019 USD ($) ft² property state	Dec. 31, 2019 GBP (£) ft² property state
Real Estate [Line Items]
Number of properties | property	244	244	789	789
Leasable square feet (sq ft) | ft²	9,197,360	9,197,360	13,736,272	13,736,272
Investment | $	$ 2,307,281		$ 3,715,237
Weighted average lease term (years)	13 years 2 months 12 days	13 years 2 months 12 days	13 years 6 months	13 years 6 months
Initial average cash lease yield (percent)	5.90%	5.90%	6.40%	6.40%
New properties
Real Estate [Line Items]
Number of properties, new | property	226	226	771	771
Leasable square feet (sq ft) | ft²	7,596,265	7,596,265	13,214,099	13,214,099
Investment | $	$ 2,223,154		$ 3,658,652
Weighted average lease term (years)	13 years 2 months 12 days	13 years 2 months 12 days	13 years 4 months 24 days	13 years 4 months 24 days
Initial average cash lease yield (percent)	5.90%	5.90%	6.40%	6.40%
New properties | U.S.
Real Estate [Line Items]
Number of properties, new | property	202	202	753	753
Number of states | state	30	30	45	45
Leasable square feet (sq ft) | ft²	5,476,009	5,476,009	11,630,423	11,630,423
Investment | $	$ 1,302,220		$ 2,860,806
Weighted average lease term (years)	14 years 10 months 24 days	14 years 10 months 24 days	13 years	13 years
Initial average cash lease yield (percent)	5.80%	5.80%	6.80%	6.80%
New properties | U.K.
Real Estate [Line Items]
Number of properties, new | property	24	24	18	18
Leasable square feet (sq ft) | ft²	2,120,256	2,120,256	1,583,676	1,583,676
Investment	$ 920,934	£ 707.8	$ 797,846	£ 625.8
Weighted average lease term (years)	10 years 9 months 18 days	10 years 9 months 18 days	15 years 7 months 6 days	15 years 7 months 6 days
Initial average cash lease yield (percent)	6.10%	6.10%	5.20%	5.20%
Properties under development | U.S.
Real Estate [Line Items]
Number of properties, under development | property	18	18	18	18
Leasable square feet (sq ft) | ft²	1,601,095	1,601,095	522,173	522,173
Investment | $	$ 84,127		$ 56,585
Weighted average lease term (years)	15 years 3 months 18 days	15 years 3 months 18 days	15 years 1 month 6 days	15 years 1 month 6 days
Initial average cash lease yield (percent)	5.60%	5.60%	7.30%	7.30%