Senior Unsecured Notes and Secured Debt (Details 1) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Debt Instrument [Line Items]
Debt issued, unsecured	$ 545,074	$ 0
Debt issued, secured	44,606	161,799
Long-term Debt, ending balance	10,923,832
Senior Unsecured Notes
Debt Instrument [Line Items]
Long-term Debt, beginning balance	8,417,447	8,260,038
Debt issued, unsecured	550,000	0
Debt extinguished	(450,000)	0
Foreign currency	(55,693)	83,101
Long-term Debt, ending balance	$ 8,461,754	$ 8,343,139
Weighted average interest rate
Rate of debt, beginning balance	4.306%	4.245%
Rate on debt issued	0.04250	0.00000
Rate on notes extinguished	0.02250	0.00000
Rate on notes foreign currency	0.04022	0.04320
Rate of debt, ending balance	4.456%	4.276%
Secured Debt
Debt Instrument [Line Items]
Long-term Debt, beginning balance	$ 2,618,408	$ 3,465,066
Debt issued, secured	44,606	161,799
Debt assumed	85,192	23,094
Principal payments	(28,385)	(32,206)
Debt extinguished	(196,573)	(987,923)
Foreign currency	(61,170)	44,859
Long-term Debt, ending balance	$ 2,462,078	$ 2,674,689
Weighted average interest rate
Rate of debt, beginning balance	3.761%	4.094%
Rate on debt issued	0.03384	0.02331
Rate on secured debt assumed	0.04395	0.06670
Rate on secured debt principal payment	0.03912	0.04378
Rate on notes extinguished	0.05658	0.05370
Rate on notes foreign currency	0.03325	0.03116
Rate of debt, ending balance	3.755%	3.669%