Quarterly report pursuant to Section 13 or 15(d)

Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Long-Term Incentive Plan Awards) (Narrative) (Details)

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Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Long-Term Incentive Plan Awards) (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended
Mar. 22, 2019
Apr. 20, 2018
Apr. 04, 2017
Mar. 08, 2016
Jun. 05, 2015
Sep. 30, 2020
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
Shares granted         800,000 172,495  
Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Total unrecognized compensation cost           $ 0 $ 0
2016 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
Dividends paid, percent representing common unit of limited partnership interest             10.00%
Dividends paid, percent payable upon vesting of LTIP Unit             90.00%
Unvested LTIP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Total unrecognized compensation cost           $ 9,300,000 $ 9,300,000
Total unrecognized compensation cost, period of recognition             2 years 4 months 24 days
2016 TBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             75,578
2016 OPP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
TSR percent             50.00%
2016 PBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             11,155
2017 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares forfeited and cancelled             369,924
2017 OPP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
TSR percent             36.00%
2017 PBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             21,492
2017 TBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             76,705
2018 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares forfeited and cancelled             102,639
2018 OPP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
TSR percent             36.00%
2018 PBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             542,651
2018 TBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             177,179
2019 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares forfeited and cancelled             175,570
2019 TBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             140,995
2019 PBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             249,058
2019 OPP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
TSR percent             36.00%
2020 OPP [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
TSR percent             36.00%
2020 PBV LTIP Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares granted             720,314
Other Executive Officers [Member] | 2016 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award       40.00%      
Remaining percent of the award       60.00%      
Other Executive Officers [Member] | 2017 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award     40.00%        
Remaining percent of the award     60.00%        
Other Executive Officers [Member] | 2018 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award   50.00%          
Remaining percent of the award   50.00%          
Messieur Rudin, Messieur DeMarco, And Messieur Tycher [Member] | 2016 LTIP Awards [Member] | Time-Based Award [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award       25.00%      
Performance period             3 years
Messieur Rudin, Messieur DeMarco, And Messieur Tycher [Member] | 2016 LTIP Awards [Member] | Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Remaining percent of the award       75.00%      
Messieur Rudin, Messieur DeMarco, And Messieur Tycher [Member] | 2017 LTIP Awards [Member] | Time-Based Award [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award     25.00%        
Performance period             3 years
Messieur Rudin, Messieur DeMarco, And Messieur Tycher [Member] | 2017 LTIP Awards [Member] | Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Remaining percent of the award     75.00%        
Messieur DeMarco And Messieur Tycher [Member] | 2018 LTIP Awards [Member] | Time-Based Award [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award   25.00%          
Performance period             3 years
Messieur DeMarco And Messieur Tycher [Member] | 2018 LTIP Awards [Member] | Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Remaining percent of the award   75.00%          
Messr DeMarco, CEO [Member] | 2019 LTIP Awards [Member] | Time-Based Award [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award 25.00%            
Messr DeMarco, CEO [Member] | 2019 LTIP Awards [Member] | Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Remaining percent of the award 75.00%            
Messr DeMarco, CEO [Member] | 2019 TBV LTIP Units [Member] | Time-Based Award [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Performance period             3 years
Messieur Tycher, Smetana, Wagner, Cardoso, And Hilton [Member] | 2019 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award 50.00%            
Remaining percent of the award 50.00%            
Messieur DeBari [Member] | 2019 LTIP Awards [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Percent of the award             100.00%