Summary of Significant Accounting Policies (Details 2)	12 Months Ended
Dec. 31, 2011 form
Share-Based Compensation
Forms of share-based compensation issued in 2010 and 2011	2
Market concentration premium
Intangible assets and deferred revenue on real estate acquisitions
Period during which intangible assets will be amortized (in years)	40

The useful life of all finite-lived intangible assets.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 12, 13, 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 30

-Section 35

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6904245&loc=d3e15372-109273

Name:	us-gaap_FiniteLivedIntangibleAssetsUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration