Senior Unsecured Notes and Secured Debt (Details 2) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Secured debt principal activity
Secured debt issued	$ 145,713	$ 60,470
Secured debt extinguished	272,399	20,285
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	2,300,521	1,867,697	2,108,373	1,133,715
Secured debt transferred	0	0
Secured debt issued	145,713	60,470
Secured debt assumed	311,653	693,797
Secured debt extinguished	(237,259)	0
Secured debt foreign currency	288	0
Secured debt principal payments	$ (28,247)	$ (20,285)
Secured debt principal balance average rate	0.0542	0.0552	0.0534	0.0559
Secured debt principal transferred average rate	0.00	0.00
Secured debt principal issued average rate	0.0413	0.0577
Secured debt principal assumed average rate	0.0571	0.0540
Secured debt principal extinguished average rate	0.0429	0.00
Secured debt principal foreign currency average rate	0.0562	0.00
Secured debt principal payment average rate	0.0535	0.0583