Senior Unsecured Notes and Secured Debt (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Secured debt principal activity
Secured debt issued	$ 71,340	$ 139,395
Secured debt extinguished	73,557	252,135
Excluding Fair Value Adjustments [Member]
Secured debt principal activity
Secured debt principal balance	2,839,025	2,285,443	2,311,586	2,108,373
Secured debt transferred	0	0
Secured debt issued	71,340	139,395
Secured debt assumed	536,856	284,988
Secured debt extinguished	(49,156)	(229,207)
Secured debt foreign currency	(6,892)	0
Secured debt principal payments	$ (24,709)	$ (18,106)
Secured debt principal balance average rate	0.0508	0.0545	0.0514	0.0534
Secured debt principal transferred average rate	0.00	0.00
Secured debt principal issued average rate	0.0496	0.0443
Secured debt principal assumed average rate	0.0422	0.0568
Secured debt principal extinguished average rate	0.0420	0.0422
Secured debt principal foreign currency average rate	0.0387	0.00
Secured debt principal payment average rate	0.0539	0.0555