Senior Unsecured Notes and Secured Debt - Summary of Principal Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Amount
Debt issued	$ 713,907	$ 0
Debt issued	0	44,921
Ending balance	14,615,764
Secured debt
Amount
Beginning balance	2,378,073	2,993,342
Debt issued	0	44,921
Debt extinguished	(41,933)	(16,040)
Principal payments	(15,955)	(15,526)
Foreign currency	15,987	(102,059)
Ending balance	$ 2,336,172	$ 2,904,638
Weighted Avg. Interest Rate
Beginning balance	3.27%	3.63%
Debt issued	0	0.0258
Debt extinguished	0.0760	0.0451
Principal payments	0.0359	0.0378
Foreign currency	0.0292	0.0327
Ending balance	3.14%	3.63%
Senior unsecured notes
Amount
Beginning balance	$ 11,509,533	$ 10,427,562
Debt issued	750,000	0
Foreign currency	20,059	(120,689)
Ending balance	$ 12,279,592	$ 10,306,873
Weighted Avg. Interest Rate
Beginning balance	3.67%	4.03%
Debt issued	0.0280	0
Foreign currency	0.0390	0.0415
Ending balance	3.62%	3.97%