Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies 2 (Details)

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Summary of Significant Accounting Policies 2 (Details)
 12 Months Ended
Dec. 31, 2012
Properties  
Period after the cessation of major construction activities for considering property as operational if leases have not commenced earlier (in years) 1 year
Period after the cessation of major constuction activities for considering property as partially operational if leases have commenced earlier (in years) 1 year
Cash and Cash Equivalents  
Maximum term until orginal maturity to classify cash and liquid investments as cash and cash equivalent (in months) 3 months
Minimum | Buildings and building improvements
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 10 years
Minimum | Land improvements
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 10 years
Minimum | Equipment and personal property
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 3 years
Maximum | Buildings and building improvements
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 40 years
Maximum | Land improvements
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 20 years
Maximum | Equipment and personal property
  
Property, Plant and Equipment [Line Items]  
Estimated useful life 10 years