Quarterly report pursuant to Section 13 or 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
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Jun. 30, 2020
Dec. 31, 2019
Jun. 30, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested stock outstanding 52,974 24,200 52,974 24,200 17,076 42,690 26,136 67,289
Dividends declared per common share $ 0 $ 0.20 $ 0.40 $ 0.60        
Mack-Cali Realty LP [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Distribution declared per common unit $ 0 $ 0.20 $ 0.40 $ 0.60        
Unvested Restricted Stock [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested stock outstanding 52,974 24,200 52,974 24,200        
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 24,200 52,974 24,200        
Unvested LTIP Units [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested stock outstanding 1,738,065 1,826,331 1,738,065 1,826,331        
Unvested LTIP Units [Member] | Mack-Cali Realty LP [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested performance shares     1,738,065 1,826,331        
Unvested AO LTIP Units [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested stock outstanding 625,000 625,000 625,000 625,000        
Unvested AO LTIP Units [Member] | Mack-Cali Realty LP [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unvested stock outstanding 625,000 625,000 625,000 625,000