Senior Unsecured Notes and Secured Debt (Summary of Secured Debt Principal Activity) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Secured debt principal activity
Debt issued	$ 45,447	$ 241,772	$ 460,015
Long-term Debt, Amount, ending balance	12,185,695
Secured Debt
Secured debt principal activity
Long-term Debt, Amount, beginning balance	2,618,408	3,465,066	3,478,207
Debt issued	45,447	241,772	460,015
Debt assumed	292,887	23,094	60,898
Debt extinguished	(306,553)	(1,080,268)	(489,293)
Debt deconsolidated	0	(60,000)	0
Principal payments	(56,288)	(64,078)	(74,466)
Foreign currency	(108,190)	92,822	29,705
Long-term Debt, Amount, ending balance	$ 2,485,711	$ 2,618,408	$ 3,465,066
Weighted average interest rate
Weighted Avg. Interest Rate, beginning balance	3.76%	4.09%	4.44%
Debt issued, weighted avg. interest rate	0.0340	0.0282	0.0265
Debt assumed, weighted avg. interest rate	0.0464	0.0667	0.0430
Debt extinguished, weighted avg. interest rate	0.0536	0.0525	0.0511
Debt deconsolidated, weighted avg. interest rate	0	0.0380	0
Principal payments, weighted avg. interest rate	0.0391	0.0434	0.0466
Foreign currency, weighted avg. interest rate	0.0333	0.0316	0.0367
Weighted Avg. Interest Rate, ending balance	3.90%	3.76%	4.09%