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
	Jun. 12, 2020	Jun. 12, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
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			5,113	5,952	13,494	15,663
Deferred stock units converted	61,277	193,949
Deferred stock units outstanding			32,659		32,659		17,854