Notes Payable - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Oct. 31, 2022 USD ($)	Sep. 30, 2022 GBP (£)	Jan. 31, 2022 GBP (£)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 GBP (£)	Jul. 31, 2021 GBP (£)	Oct. 31, 2020 GBP (£)
Notes payable
Debt
Unamortized net premiums | $	$ 241,300,000		$ 241,300,000					$ 295,500,000
Deferred financing costs | $	$ 56,600,000		$ 56,600,000					$ 53,100,000
Weighted average interest rate (as a percent)	3.30%		3.30%			3.30%
Weighted average remaining years until maturity			7 years 3 months 18 days
Interest incurred on notes and bonds | $	$ 107,900,000	$ 65,800,000	$ 314,000,000	$ 191,700,000
Notes payable | 1.625% Notes due 2030
Debt
Principal amount						£ 400,000,000					£ 400,000,000
Interest rate (as a percent)	1.625%		1.625%			1.625%					0.01625%
Notes payable | 1.125% Notes due 2027
Debt
Principal amount						£ 400,000,000			£ 400,000,000	£ 400,000,000
Interest rate (as a percent)	1.125%		1.125%			1.125%			1.125%	0.01125%
Notes payable | 1.750% Notes due 2033
Debt
Principal amount						£ 350,000,000			£ 350,000,000	£ 350,000,000
Interest rate (as a percent)	1.75%		1.75%			1.75%			1.75%	0.0175%
Notes payable | 1.875% Notes due 2027
Debt
Principal amount						£ 250,000,000	£ 250,000,000
Interest rate (as a percent)	1.875%		1.875%			1.875%	0.01875%
Notes payable | 2.500% Notes due 2042
Debt
Principal amount						£ 250,000,000	£ 250,000,000
Interest rate (as a percent)	2.50%		2.50%			2.50%	0.025%
Notes payable | Maximum
Debt
Debt to total adjusted assets ratio (as a percent)			60.00%
Secured debt to total adjusted assets ratio (as a percent)			40.00%
Notes payable | Minimum
Debt
Debt service coverage ratio			1.5
Total unencumbered assets as a percentage of outstanding unsecured debt			150.00%
Unsecured debt | 5.625% Notes due 2032 | Subsequent event
Debt
Principal amount | $					$ 750,000,000
Interest rate (as a percent)					5.625%