Annual report pursuant to Section 13 and 15(d)

Recent Transactions (Consolidations) (Narrative) (Details)

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Recent Transactions (Consolidations) (Narrative) (Details)
12 Months Ended
Jan. 31, 2019
USD ($)
item
Jan. 30, 2019
USD ($)
Aug. 02, 2018
USD ($)
item
Dec. 31, 2019
USD ($)
item
Dec. 31, 2018
USD ($)
item
Dec. 31, 2017
USD ($)
Aug. 01, 2018
USD ($)
Real Estate Properties [Line Items]              
Number of units | item       208 1,317    
Purchase price of property       $ 97,504,000 $ 112,511,000 $ 90,422,000  
Mortgage loan         45,242,000 $ 45,734,000  
Gain on change of control of interests       13,790,000 14,217,000    
Issuance of loan       43,300,000 30,400,000    
Loan balance       2,808,517,000 2,792,651,000    
Noncontrolling interest's fair value       205,776,000 210,523,000    
Mack-Cali Realty LP [Member]              
Real Estate Properties [Line Items]              
Purchase price of property       97,504,000 112,511,000    
Gain on change of control of interests       $ 13,790,000 14,217,000    
Marbella Tower Urban Renewal Associates LLC [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in venture             24.27%
Percentage of additional interest acquired     50.00%        
Number of units | item     412        
Purchase price of property     $ 65,600,000        
Mortgage loan, maturity month and year       August 2026      
Spread over LIBOR     4.07%        
Mortgage loan     $ 131,000,000       $ 95,000,000
Gain on change of control of interests       $ 14,200,000      
Repayment of mortgage loans     $ 95,000,000        
Issuance of loan         $ 37,400,000    
Loan balance       14,000,000      
Noncontrolling interest's fair value       $ 29,800,000      
Unconsolidated Joint Venture Multi-Family Properties [Member]              
Real Estate Properties [Line Items]              
Number of units | item       2,611      
Unconsolidated Joint Venture Multi-Family Properties [Member] | Marbella Tower Urban Renewal Associates LLC [Member]              
Real Estate Properties [Line Items]              
Percentage of interest in venture 74.27% 24.27% 74.27%       24.27%
Percentage of additional interest acquired 50.00% 50.00% 50.00%        
Number of units | item 311            
Purchase price of property $ 77,500,000            
Mortgage loan, maturity month and year       August 2026      
Spread over LIBOR 4.20%            
Mortgage loan $ 117,000,000 $ 74,700,000          
Gain on change of control of interests       $ 13,800,000      
Repayment of mortgage loans $ 74,700,000            
Loan balance       15,300,000      
Noncontrolling interest's fair value       $ 13,700,000