Senior Unsecured Notes and Secured Debt - Summary of Principal Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Amount
Debt issued, unsecured	$ 1,036,964	$ 0
Debt issued, secured	247,163	20,326
Ending balance	12,410,495
Senior Unsecured Notes
Amount
Beginning balance	9,699,984	8,417,447
Debt issued, unsecured	1,050,000	0
Debt extinguished	(1,050,000)	(450,000)
Foreign currency	37,553	39,542
Ending balance	$ 9,737,537	$ 8,006,989
Weighted Avg. Interest Rate
Beginning balance	4.48%	4.31%
Debt issued	0.0389	0.0000
Debt extinguished	0.0498	0.0225
Foreign currency	0.0433	0.0522
Ending balance	4.35%	4.45%
Secured debt
Amount
Beginning balance	$ 2,485,711	$ 2,618,408
Debt issued, secured	247,163	20,326
Debt assumed	42,000	85,192
Debt extinguished	(114,570)	(183,408)
Principal payments	(13,543)	(14,247)
Foreign currency	26,197	(27,876)
Ending balance	$ 2,672,958	$ 2,498,395
Weighted Avg. Interest Rate
Beginning balance	3.90%	3.76%
Debt issued	0.0368	0.0377
Debt assumed	0.0462	0.0440
Debt extinguished	0.0496	0.0581
Principal payments	0.0385	0.0387
Foreign currency	0.0333	0.0333
Ending balance	3.84%	3.70%