Quarterly report pursuant to Section 13 or 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) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Mar. 10, 2021
Jul. 26, 2020
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Jul. 25, 2020
May 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Weighted average remaining contractual life         4 years 3 months 18 days   3 years 7 months 6 days    
Options exercised         0 0      
Stock options expense     $ 224,000 $ 0 $ 338,000 $ 0      
Mahbod Nia, CEO [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Share price $ 15.79                
Shares Under Options - Granted 950,000                
2013 Incentive Stock Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Reserved stocks for issuance     6,565,000   6,565,000       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   $ 14.39              
MAG Partners [Member] | Maximum [Member] | Common Class At $20.00 [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Share price   $ 20.00              
Number of shares authorized   100,000              
Share price issued   $ 20.00