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Risk Management and Use of Derivative Financial Instruments - Narratives (Details) £ in Millions, ¥ in Billions	3 Months Ended
	Mar. 31, 2020 USD ($) offering	Mar. 31, 2019 USD ($)	Mar. 31, 2020 JPY (¥)	Mar. 31, 2020 EUR (€)	Mar. 31, 2020 GBP (£)	Mar. 27, 2020 USD ($)	Feb. 20, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 19, 2019
Summary of Derivative Instruments
Net collateral posted for derivatives	$ 0							$ 0
Derivative, remaining maturity	73 months
Total credit exposure on derivatives	$ 34,100,000
Derivatives, net liability position	10,200,000							9,600,000
Aggregate termination value for immediate settlement	10,800,000							9,900,000
Debt outstanding	366,604,000							201,267,000
Other comprehensive income foreign currency gain (loss)	84,900,000	$ 44,100,000
Unsecured Revolving Credit Facility
Summary of Derivative Instruments
Debt outstanding	75,483,000							201,267,000
Unsecured Term Loans
Summary of Derivative Instruments
Debt outstanding	291,121,000							0
EUR \| Unsecured Revolving Credit Facility
Summary of Derivative Instruments
Debt outstanding	43,276,000			€ 39,500,000				131,438,000
EUR \| Unsecured Term Loans
Summary of Derivative Instruments
Debt outstanding	105,726,000			96,500,000		$ 105,900,000		0
JPY \| Unsecured Revolving Credit Facility
Summary of Derivative Instruments
Debt outstanding	22,207,000		¥ 2.4					22,295,000
GBP \| Unsecured Revolving Credit Facility
Summary of Derivative Instruments
Debt outstanding	0							47,534,000
GBP \| Unsecured Term Loans
Summary of Derivative Instruments
Debt outstanding	$ 185,395,000				£ 150.0		$ 193,100,000	$ 0
Unsecured senior notes
Summary of Derivative Instruments
Number of offerings completed \| offering	5
Principal amount	$ 4,400,000,000
Unsecured senior notes \| 2.0% Senior Notes due 2023
Summary of Derivative Instruments
Principal amount \| €				€ 500,000,000.0
Coupon rate (percentage)	2.00%		2.00%	2.00%	2.00%
Unsecured senior notes \| 2.25% Senior Notes due 2024
Summary of Derivative Instruments
Principal amount \| €				€ 500,000,000.0
Coupon rate (percentage)	2.25%		2.25%	2.25%	2.25%
Unsecured senior notes \| 2.250% Senior Notes due 2026
Summary of Derivative Instruments
Principal amount \| €				€ 500,000,000.0
Coupon rate (percentage)	2.25%		2.25%	2.25%	2.25%
Unsecured senior notes \| 2.125% Senior Notes due 2027
Summary of Derivative Instruments
Principal amount \| €				€ 500,000,000.0
Coupon rate (percentage)	2.125%		2.125%	2.125%	2.125%
Unsecured senior notes \| 1.350% Senior Notes due 2028
Summary of Derivative Instruments
Principal amount \| €				€ 500,000,000.0
Coupon rate (percentage)	1.35%		1.35%	1.35%	1.35%				1.35%
Individual Counterparty
Summary of Derivative Instruments
Total credit exposure on derivatives	$ 9,300,000
Interest expense
Summary of Derivative Instruments
Estimated amount reclassified from OCI to expense (gain)	2,800,000
Other gains
Summary of Derivative Instruments
Estimated amount reclassified from OCI to expense (gain)	$ (11,800,000)