Senior Unsecured Notes and Secured Debt (Details 2) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Secured debt principal activity
Secured debt issued	$ 193,541	$ 222,612
Secured debt extinguished	471,898	469,455
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	3,300,642	2,945,697	$ 3,478,207	$ 2,941,765
Secured debt issued	193,541	222,612
Secured debt assumed	47,156	339,929
Secured debt extinguished	(416,009)	(420,672)
Secured debt principal payments	(55,889)	(48,783)
Secured debt foreign currency	$ 53,636	$ (89,154)
Secured debt principal balance average rate	0.04272	0.0472	0.0444	0.0494
Secured debt principal issued average rate	0.03053	0.0276
Secured debt principal assumed average rate	0.04132	0.0334
Secured debt principal extinguished average rate	0.04986	0.0427
Secured debt principal payment average rate	0.04478	0.0485
Secured debt principal foreign currency average rate	0.03631	0.0388