Annual report pursuant to Section 13 and 15(d)

Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (AO LTIP Units (Appreciation-Only LTIP Units)) (Narrative) (Details)

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Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (AO LTIP Units (Appreciation-Only LTIP Units)) (Narrative) (Details) - USD ($)
12 Months Ended
Jun. 05, 2015
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares granted 800,000      
Share price $ 17.31      
Exercisable period   10 years    
Common stock trading days   30 days    
Common stock trade share price $ 25.00      
Share price - weighted average fair value of options granted   $ 2.95    
Stock options expense   $ 446,000 $ 0 $ 193,000
AO LTIP Units Award [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share price   $ 21.46    
Exercisable period   10 years    
Share price - weighted average fair value of options granted     $ 3.98  
Total unrecognized compensation cost   $ 1,400,000    
Total unrecognized compensation cost, period of recognition   2 years 2 months 12 days    
Stock options expense   $ 622,000 $ 498,000 $ 0
AO LTIP Units Award [Member] | Messr DeMarco, CEO [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares granted   625,000 625,000  
Income allocation   10.00%    
Percent of cash distribution   10.00%    
AO LTIP Units Award [Member] | Messr DeMarco, CEO [Member] | Tranche One [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares to be vested and exercisable   250,000    
Common stock trading days   30 days    
Common stock trade share price   $ 25.00    
Common stock expiration date   Mar. 13, 2023    
AO LTIP Units Award [Member] | Messr DeMarco, CEO [Member] | Tranche Two [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares to be vested and exercisable   250,000    
Common stock trading days   30 days    
Common stock trade share price   $ 28.00    
AO LTIP Units Award [Member] | Messr DeMarco, CEO [Member] | Tranche Three [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares to be vested and exercisable   125,000    
Common stock trading days   30 days    
Common stock trade share price   $ 31.00