Senior Unsecured Notes and Secured Debt (Summary of Senior Unsecured Note Principal Activity) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Amount
Debt issued	$ 3,974,559	$ 2,824,176	$ 7,500
Ending balance	13,420,904
Senior Unsecured Notes
Amount
Beginning balance	9,699,984	8,417,447	8,260,038
Debt issued	3,987,790	2,850,000	7,500
Debt extinguished	(3,335,290)	(1,450,000)	(5,000)
Foreign currency	75,078	(117,463)	154,909
Ending balance	$ 10,427,562	$ 9,699,984	$ 8,417,447
Weighted Avg. Interest Rate
Beginning balance	4.48%	4.31%	4.25%
Debt issued	0.0334	0.0457	0.0197
Debt extinguished	0.0439	0.0346	0.0183
Foreign currency	0.0422	0.0416	0.0429
Ending balance	4.03%	4.48%	4.31%