Assets Held for Sale and Discontinued Operations (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012 Units Property	Dec. 31, 2011 Units Property	Dec. 31, 2010 Units Property
Discontinued Operations And Assets Held For Sale (Textual) [Abstract]
Number of properties classified as held for sale	0	75
Number of units in properties classified as held for sale		11,232
Number of consolidated properties disposed	75	67	51
Number of properties to be sold period for evaluation	12 months
Number of units in consolidated properties disposed	11,232	10,912	8,189
Prepayment penalties treated as reduction of gain upon repayment of property loans collateralized by properties sold	$ 16.5	$ 14.9	$ 4.5
Goodwill written off related to properties sold or classified as held for sale	$ 7.5	$ 5.1	$ 4.7

Write-off of the carrying amount of goodwill associated with all or a portion of a reporting unit that is sold in the period.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 72

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

-Clause 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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_GoodwillWrittenOffRelatedToSaleOfBusinessUnit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration