Non-Recourse Property Debt (Details Textual) (USD $) In Millions, unless otherwise specified				12 Months Ended
	Dec. 31, 2011 Property Notes Payable [Member] Property	Dec. 31, 2011 Total rate of return swaps [Member] Property	Dec. 31, 2010 Total rate of return swaps [Member] Property	Dec. 31, 2011 Property tax-exempt bonds payable [Member] Property	Dec. 31, 2011 Property tax-exempt bonds payable [Member] Total rate of return swaps [Member]
Non-Recourse Property Debt (Textual) [Abstract]
Number of properties collateralizing property debt	297	4	12	29
Gross book Value of Properties Collateralizing Property Debt	$ 8,176.0			$ 695.9
Weighted average fixed receive rate under total rate of return swaps					5.80%
Weighted average variable rate under total rate of return swaps					2.60%
Carrying amount of fixed rate property debt converted to variable rates using total rate of return swaps				$ 69.2