Annual report pursuant to Section 13 and 15(d)

Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Stock Option Plans) (Narrative) (Details)

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Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Stock Option Plans) (Narrative) (Details)
12 Months Ended
Jun. 05, 2015
item
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
May 31, 2013
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Weighted average remaining contractual life   3 years 7 months 6 days 5 years 4 months 24 days    
Share price | $ / shares $ 17.31        
Proceeds from stock options exercised | $   $ 0 $ 0 $ 0  
Stock options expense | $   $ 446,000 $ 0 $ 193,000  
Shares Under Options - Granted 800,000        
Common stock trade share price | $ / shares $ 25.00        
Annual installments | item 3        
Exercisable period   10 years      
Common stock trading days   30 days      
Share price - weighted average fair value of options granted | $ / shares   $ 2.95      
Three Equal Annual Installment [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares Under Options - Granted 400,000        
Common Stock Trades [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares Under Options - Granted 400,000        
2013 Incentive Stock Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Reserved stocks for issuance         4,600,000
MAG Partners [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares Under Options - Granted   157,505      
MAG Partners [Member] | Maximum [Member] | Common Class At $14.39 [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of shares authorized   230,000      
Share price issued | $ / shares   $ 14.39      
MAG Partners [Member] | Maximum [Member] | Common Class At $20.00 [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of shares authorized   100,000      
Share price issued | $ / shares   $ 20.00