Senior Unsecured Notes and Secured Debt (Details 2) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Secured debt principal activity
Secured debt issued	$ 460,015	$ 228,685	$ 109,503
Secured debt extinguished	563,759	573,390	341,839
Secured Debt [Member]
Secured debt principal activity
Secured debt principal balance	3,465,066	3,478,207	2,941,765	$ 3,010,711
Secured debt issued	460,015	228,685	109,503
Secured debt assumed	60,898	1,007,482	204,949
Secured debt extinguished	(489,293)	(506,326)	(279,559)
Secured debt foreign currency	29,705	(126,335)	(41,559)
Secured debt principal payments	$ (74,466)	$ (67,064)	$ (62,280)
Secured debt principal balance average rate	0.04094	0.0444	0.0494	0.05095
Secured debt principal issued average rate	0.02646	0.02776	0.03374
Secured debt principal assumed average rate	0.04301	0.03334	0.0475
Secured debt principal extinguished average rate	0.05105	0.04506	0.04824
Secured debt principal payment average rate	0.04663	0.04801	0.0493
Secured debt principal foreign currency average rate	0.0367	0.03834	0.03811