Annual report pursuant to Section 13 and 15(d)

Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Earnings Per Share/Unit) (Narrative) (Details)

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Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Earnings Per Share/Unit) (Narrative) (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 52,974 42,690 67,289 108,318
Dividends declared per common share $ 0.40 $ 0.80 $ 0.80  
Mack-Cali Realty LP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Distribution declared per common unit $ 0.40 $ 0.80 $ 0.80  
Unvested Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 52,974 42,690 67,289  
Unvested Restricted Stock [Member] | Mack-Cali Realty LP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 52,974 42,690 67,289  
Unvested LTIP Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 1,722,929 1,826,331 1,707,106  
Unvested LTIP Units [Member] | Mack-Cali Realty LP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 1,722,929 1,826,331 1,707,106  
Unvested AO LTIP Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 625,000 625,000    
Unvested AO LTIP Units [Member] | Mack-Cali Realty LP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unvested stock outstanding 625,000 625,000