Senior Unsecured Notes and Secured Debt (Details 2) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Secured debt principal activity
Secured debt issued	$ 12,536	$ 75,136
Secured debt extinguished	822,438	130,343
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	2,665,477	3,488,488	$ 3,465,066	$ 3,478,207
Secured debt issued	12,536	75,136
Secured debt extinguished	(806,189)	(111,701)
Secured debt principal payments	10,313	65,488
Secured debt foreign currency	$ (16,249)	$ (18,642)
Secured debt principal balance average rate	0.03744	0.044	0.04094	0.0444
Secured debt principal issued average rate	0.0234	0.0306
Secured debt principal extinguished average rate	0.0558	0.0445
Secured debt principal payment average rate	0.03262	0.03669
Secured debt principal foreign currency average rate	0.04469	0.04539