Quarterly report pursuant to Section 13 or 15(d)

Commitments And Contingencies (Management Changes) (Narrative) (Details)

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Commitments And Contingencies (Management Changes) (Narrative) (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jul. 26, 2020
Jul. 25, 2020
Jun. 05, 2015
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Commitments And Contingencies [Line Items]                
Shares granted     800,000          
General and administrative       $ 17,242,000 $ 16,946,000 $ 33,060,000 $ 30,265,000  
Accounts payable, accrued expenses and other liabilities       217,875,000   $ 217,875,000   $ 209,510,000
Common stock trading days           30 days    
Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
General and administrative       17,242,000 $ 16,946,000 $ 33,060,000 $ 30,265,000  
Accounts payable, accrued expenses and other liabilities       $ 217,875,000   $ 217,875,000   $ 209,510,000
Subsequent Event [Member] | MAG Partners [Member]                
Commitments And Contingencies [Line Items]                
Monthly fee   $ 150,000            
One-time bonus   300,000            
One-time completion bonus   $ 200,000            
Shares granted 157,505              
Legal fees $ 10,000              
Common Class At $14.39 [Member] | Maximum [Member] | Subsequent Event [Member] | MAG Partners [Member]                
Commitments And Contingencies [Line Items]                
Number of shares authorized   230,000            
Share price $ 14.39              
Common Class At $20.00 [Member] | Maximum [Member] | Subsequent Event [Member] | MAG Partners [Member]                
Commitments And Contingencies [Line Items]                
Number of shares authorized 100,000              
Share price $ 20.00