Senior Unsecured Notes and Secured Debt (Summary of Secured Debt Principal Activity) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Amount
Debt issued	$ 343,696	$ 45,447	$ 241,772
Ending balance	13,420,904
Secured Debt
Amount
Beginning balance	2,485,711	2,618,408	3,465,066
Debt issued	343,696	45,447	241,772
Debt assumed	385,145	292,887	23,094
Debt extinguished	(230,108)	(306,553)	(1,080,268)
Debt deconsolidated	0	0	(60,000)
Principal payments	(54,325)	(56,288)	(64,078)
Foreign currency	63,223	(108,190)	92,822
Ending balance	$ 2,993,342	$ 2,485,711	$ 2,618,408
Weighted Avg. Interest Rate
Beginning balance	3.90%	3.76%	4.09%
Debt issued	0.0311	0.0340	0.0282
Debt assumed	0.0434	0.0464	0.0667
Debt extinguished	0.0435	0.0536	0.0525
Debt deconsolidated	0	0	0.0380
Principal payments	0.0375	0.0391	0.0434
Foreign currency	0.0328	0.0333	0.0316
Ending balance	3.63%	3.90%	3.76%