Senior Unsecured Notes and Secured Debt (Details 2) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Secured debt principal activity
Secured debt issued	$ 161,992	$ 136,801
Secured debt extinguished	281,051	323,950
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	3,421,266	3,033,871	$ 3,478,207	$ 2,941,765
Secured debt issued	161,992	136,801
Secured debt assumed	0	317,897
Secured debt extinguished	(243,314)	(290,984)
Secured debt principal payments	(37,737)	(32,966)
Secured debt foreign currency	$ 62,118	$ (38,642)
Secured debt principal balance average rate	0.04328	0.0475	0.0444	0.0494
Secured debt principal issued average rate	0.03051	0.02845
Secured debt principal assumed average rate	0	0.03223
Secured debt principal extinguished average rate	0.04874	0.04208
Secured debt principal payment average rate	0.04579	0.04775
Secured debt principal foreign currency average rate	0.03652	0.03994