cm:Concept: us-gaap:NoncontrollingInterestInNetIncomeLossOperatingPartnershipsNonredeemable
       
          
          | Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Nonredeemable | 
       
       
          
          | us-gaap:NoncontrollingInterestInNetIncomeLossOperatingPartnershipsNonredeemable | 
       
       
          
          | Amount after tax of income (loss) attributable to nonredeemable noncontrolling partner in an operating partnership. | 
       
       
          
          | cm:Concept | 
       
       
          
          | Monetary (xbrli:monetaryItemType) | 
       
       
          
          | For Period (duration) | 
       
       
          
          | Debit | 
       
       
          
          | false | 
       
       
          
          | us-gaap:NoncontrollingInterestInNetIncomeLossOperatingPartnershipsNonredeemable |