Quarterly report pursuant to Section 13 or 15(d)

Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Deferred Stock Compensation Plan For Directors) (Narrative) (Details)

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Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital (Deferred Stock Compensation Plan For Directors) (Narrative) (Details) - shares
 3 Months Ended 9 Months Ended 12 Months Ended
Jun. 12, 2020
Jun. 12, 2019
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Dec. 31, 2019
Mack-Cali Realty Corporation Stockholders' Equity And Mack-Cali Realty, L.P.'s Partners' Capital [Abstract]            
Maximum percentage of retainer fee that directors may defer         100.00%  
Deferred stock units earned     5,952 3,724 15,663 10,767
Deferred stock units converted 61,277 193,949        
Deferred stock units outstanding     11,902   11,902 59,899