Organization (Details)	12 Months Ended
Dec. 31, 2011 properties
Organization, Consolidation and Presentation of Financial Statements
Entity Incorporate, Date of Incorporation, Year	1991
Number of States in which Entity Operates	24

The number of states the entity operates in as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant