Basis of Presentation (Details) (Joint ventures)	9 Months Ended
	Sep. 30, 2012 entity
Principles of Consolidation
Number of variable interest entities	9
Consolidated variable interest entities
Principles of Consolidation
Number of variable interest entities	5
Single purpose entities where the company is not the primary beneficiary
Principles of Consolidation
Number of variable interest entities	4
Minimum
Principles of Consolidation
Number of parking facilities operated	1
Maximum
Principles of Consolidation
Number of parking facilities operated	35