Senior Unsecured Notes and Secured Debt - Summary of Principal Activity (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Amount
Debt issued, unsecured	$ 2,036,964	$ 545,074
Debt issued, secured	295,969	44,606
Ending balance	13,401,538
Senior Unsecured Notes
Amount
Beginning balance	9,699,984	8,417,447
Debt issued, unsecured	2,050,000	550,000
Debt extinguished	(1,050,000)	(450,000)
Foreign currency	11,572	(55,693)
Ending balance	$ 10,711,556	$ 8,461,754
Weighted Avg. Interest Rate
Beginning balance	4.48%	4.31%
Debt issued	0.0358	0.0425
Debt extinguished	0.0498	0.0225
Foreign currency	0.0352	0.0402
Ending balance	4.24%	4.46%
Secured debt
Amount
Beginning balance	$ 2,485,711	$ 2,618,408
Debt issued, secured	295,969	44,606
Debt assumed	42,000	85,192
Debt extinguished	(151,473)	(196,573)
Principal payments	(27,227)	(28,385)
Foreign currency	45,002	(61,170)
Ending balance	$ 2,689,982	$ 2,462,078
Weighted Avg. Interest Rate
Beginning balance	3.90%	3.76%
Debt issued	0.0352	0.0338
Debt assumed	0.0462	0.0440
Debt extinguished	0.0442	0.0566
Principal payments	0.0374	0.0391
Foreign currency	0.0337	0.0333
Ending balance	3.84%	3.76%