Senior Unsecured Notes and Secured Debt (Details 2) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Secured debt principal activity
Secured debt issued	$ 228,685	$ 109,503	$ 89,208
Secured debt extinguished	573,390	341,839	674,103
Secured Debt [Member]
Secured debt principal activity
Secured debt principal balance	3,478,207	2,941,765	3,010,711	$ 2,311,586
Secured debt issued	228,685	109,503	89,208
Secured debt assumed	1,007,482	204,949	1,290,858
Secured debt extinguished	(506,326)	(279,559)	(614,375)
Secured debt foreign currency	(126,335)	(41,559)	(10,361)
Secured debt principal payments	$ (67,064)	$ (62,280)	$ (56,205)
Secured debt principal balance average rate	0.0444	0.0494	0.05095	0.0514
Secured debt principal issued average rate	0.02776	0.03374	0.04982
Secured debt principal assumed average rate	0.03334	0.0475	0.04159
Secured debt principal extinguished average rate	0.04506	0.04824	0.0373
Secured debt principal foreign currency average rate	0.03834	0.03811	0.04013
Secured debt principal payment average rate	0.04801	0.0493	0.05248