Fair Value Measurements (Details 1)	3 Months Ended
	Mar. 31, 2012 Property Y	Mar. 31, 2011 Property Y
Nonrecourse property debt:
Number of properties encumbered by nonrecourse property debt measured at fair value during period	4	8
Weighted average interest rate	5.84%	6.40%
Weighted average maturity	24.7	24.0
Weighted average loan-to-value ratio	80.20%	80.10%