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Derivatives - Narrative (Details) € in Millions, £ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Jan. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 GBP (£)	Jun. 30, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 GBP (£)	Dec. 31, 2019 EUR (€)	Jan. 31, 2019 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Investments in unconsolidated joint ventures				$ 1,791,499,000			$ 2,256,214,000
Cash Collateral Pledged	$ 14,300,000			0			0
Foreign currency risk
Derivative Instruments, Gain (Loss) [Line Items]
Investments in unconsolidated joint ventures				900,000,000	£ 267.6	€ 491.8	900,000,000	£ 275.5	€ 517.9
Forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	119,000,000									$ 100,000,000
Forward Contracts and Performance Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Deposits related to agreements included in other assets				$ 12,800,000			$ 10,000,000.0
Gain on derivative	$ 5,800,000
Three-Month LIBOR [Member] \| Non-Designated Hedges \| Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized loss on notional forward starting swap		$ 86,900,000	$ 146,100,000
Notional amount		$ 2,000,000,000.0	$ 2,000,000,000.0