Real Estate Dispositions (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Gain on Dispositions of Unconsolidated Real Estate and Other (Textuals) [Abstract]
Number of properties classified as held for sale	2		2		29
Number of units in properties classified as held for sale	710		710		4,750
Number of consolidated properties disposed			27	23	51
Number of units in consolidated properties disposed			4,040	3,547	8,189
Prepayment penalties treated as reduction of gain upon repayment of property loans collateralized by properties sold	$ 4.8	$ 2.6	$ 5.0	$ 3.2
Goodwill related to conventional and affordable segments allocated to carrying amounts of properties sold or classified as held for sale	0.9	1.5	1.7	2.8
Amount of allocated goodwill reducing gain on dispositions of real estate for properties sold or classified as held for sale	0.7		1.2
Amount of allocated goodwill treated as an adjustment of impairment losses for properties sold or classified as held for sale	0.2		0.5
Reduction of gain on dispositions of real estate		1.4		2.6
Reduction of gain on dispositions of real estate adjustment of impairment losses		$ 0.1		$ 0.2