Business Segments (Details Textuals) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011 Property	Sep. 30, 2010
Conventional [Member]
Business Segments (Textuals) [Abstract]
Number of owned real estate properties in segments	205
Number of units in owned real estate properties in segments	64,781
Capital additions related to segments	$ 111.2	$ 104.9
Affordable [Member]
Business Segments (Textuals) [Abstract]
Number of owned real estate properties in segments	201
Number of units in owned real estate properties in segments	24,040
Capital additions related to segments	$ 12.2	$ 24.0

Total expenditures for additions to long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets of the reportable segment; if the amount: (a) is included in the determination of segment assets reviewed by the chief operating decision maker or (b) is otherwise regularly provided to the chief operating decision maker, even if not included in the determination of segment assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 28

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_AdditionsToNoncurrentAssets
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration