Assets Held for Sale and Discontinued Operations (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012 Property	Mar. 31, 2011 Property	Dec. 31, 2011 Property
Discontinued Operations And Assets Held For Sale (Textual) [Abstract]
Number of properties classified as held for sale	2		12
Number of units in properties classified as held for sale	376		1,949
Number of consolidated properties disposed	10	12	67
Number of properties to be sold period for evaluation	12 months
Number of units in consolidated properties disposed	1,573	1,621	10,912
Prepayment penalties treated as reduction of gain upon repayment of property loans collateralized by properties sold	$ 1.4	$ 0.3
Goodwill related to conventional and affordable segments allocated to carrying amounts of properties sold or classified as held for sale	0.7	0.8
Amount of allocated goodwill reducing gain on dispositions of real estate for properties sold or classified as held for sale	0.6	0.6
Amount of allocated goodwill treated as an adjustment of impairment losses for properties sold or classified as held for sale	0.1	0.2
Non-recourse property debt assumed in connection with real estate dispositions	$ 8.0	$ 4.2