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 6 Months Ended 18 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 17,076 26,136 17,076 26,136 17,076 42,690 42,690 66,321 67,289
Dividends declared per common share $ 0.20 $ 0.20     $ 0.40        
Mack-Cali Realty LP [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Dividends declared per common share $ 0.20 $ 0.20 $ 0.40 $ 0.40          
Unvested Restricted Stock [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 17,076 26,136 17,076 26,136 17,076        
Unvested Restricted Stock [Member] | Mack-Cali Realty LP [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 17,076 26,136 17,076 26,136 17,076        
Unvested LTIP Units [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 2,659,518 1,826,331 2,659,518 1,826,331 2,659,518        
Unvested LTIP Units [Member] | Mack-Cali Realty LP [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested performance shares     2,659,518 1,826,331          
Unvested AO LTIP Units [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 625,000 625,000 625,000 625,000 625,000        
Unvested AO LTIP Units [Member] | Mack-Cali Realty LP [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unvested stock outstanding 625,000 625,000 625,000 625,000 625,000