Senior Unsecured Notes and Secured Debt (Details 2)	3 Months Ended		9 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Secured debt principal activity
Secured debt issued			$ 222,612,000	$ 98,100,000
Secured debt extinguished			469,455,000	286,162,000
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	$ 2,941,765,000	$ 3,010,711,000	2,945,697,000	2,861,720,000
Secured debt issued			222,612,000	98,100,000
Secured debt assumed			339,929,000	62,505,000
Secured debt extinguished			(420,672,000)	(240,355,000)
Secured debt principal payments			(48,783,000)	(23,434,000)
Secured debt foreign currency			$ (89,154,000)	$ (45,807,000)
Secured debt principal balance average rate	0.0494	0.051	0.0472	0.0494
Secured debt principal issued average rate			0.0276	0.0323
Secured debt principal assumed average rate			0.0334	0.0311
Secured debt principal extinguished average rate			0.0427	0.0566
Secured debt principal payment average rate			0.0485	0.0378
Secured debt principal foreign currency average rate			0.0388	0.0497