Investments in Real Estate - Acquisitions Allocation (Details) $ in Thousands, € in Millions, £ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2021 GBP (£)	Sep. 30, 2021 EUR (€)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 GBP (£)
Acquisitions
Weighted average amortization period for acquired lease intangible assets	13 years	13 years	13 years	17 years 6 months	17 years 6 months
Weighted average amortization period for acquired lease intangible liabilities	18 years 6 months	18 years 6 months	18 years 6 months	14 years 9 months 18 days	14 years 9 months 18 days
Real Estate Investment | U.S.
Acquisitions
Land	$ 621,000			$ 226,600
Buildings and improvements	955,000			457,600
Lease intangible assets	350,400			137,000
Other assets	379,300			19,800
Lease intangible liabilities	(42,300)			(5,400)
Other liabilities	(122,200)			(900)
Net	2,141,200			834,700
Allocated to other assets, financing receivables with above-market terms	66,900			19,100
Allocated to other assets, finance lease right-of-use assets	41,700
Allocated to other assets, investments in sales-type leases	5,500
Allocated to other assets, right-of-use assets under ground leases	265,200			$ 689
Allocated to other liabilities, deferred rent on below-market leases	21,500
Allocated to other liabilities, lease liabilities under ground leases	$ 100,700
Real Estate Investment | U.K.
Acquisitions
Land | £		£ 283.9			£ 97.5
Buildings and improvements | £		549.9			124.8
Lease intangible assets | £		173.5			83.8
Other assets | £		20.2			50.6
Lease intangible liabilities | £		(6.4)			0.0
Other liabilities | £		(0.3)			0.0
Net | £		1,020.8			356.7
Allocated to land, right of use assets under long-term ground leases | £		1.3			£ 6.5
Allocated to other assets, financing receivables with above-market terms | £		2.7
Allocated to other assets, finance lease right-of-use assets | £		£ 17.5
Real Estate Investment | Spain
Acquisitions
Land | €			€ 36.6
Buildings and improvements | €			36.3
Lease intangible assets | €			23.3
Other assets | €			0.0
Lease intangible liabilities | €			0.0
Other liabilities | €			0.0
Net | €			€ 96.2