Commitments And Contingencies (Changes In Executive Officers) (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended
Jun. 05, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Commitments And Contingencies [Line Items]                
General and administrative   $ 11,620,000     $ 13,140,000 $ 41,160,000 $ 37,223,000  
Accounts payable, accrued expenses and other liabilities   179,487,000       179,487,000   $ 192,716,000
Restructuring costs related to stock compensation           $ 1,100,000    
Shares granted           40,185    
Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
General and administrative   11,620,000     $ 13,140,000 $ 41,160,000 $ 37,223,000  
Accounts payable, accrued expenses and other liabilities   179,487,000       179,487,000   $ 192,716,000
Messr Rudin [Member]                
Commitments And Contingencies [Line Items]                
Severance benefits           $ 2,558,082    
Period for continuation of health insurance           18 months    
Payment to former executive officers     $ 1,200,000          
Payment of unreimbursed expenses           $ 50,000    
COBRA payment   34,047       34,047    
Accounts payable, accrued expenses and other liabilities     28,000          
Restructuring costs related to stock compensation     $ 1,600,000          
Messr Krug [Member]                
Commitments And Contingencies [Line Items]                
Severance benefits           1,312,500    
Prorated 2018 target bonus amount   93,750       $ 93,750    
Messr Krug [Member] | Maximum [Member]                
Commitments And Contingencies [Line Items]                
Period for continuation of health insurance           2 years    
COBRA payment   42,000       $ 42,000    
Messr DeLorenzo [Member]                
Commitments And Contingencies [Line Items]                
Severance benefits           $ 500,000    
Period for continuation of health insurance           18 months    
Messr DeLorenzo [Member] | Maximum [Member]                
Commitments And Contingencies [Line Items]                
COBRA payment   42,000       $ 42,000    
Messrs. Rudin, Krug, And DeLorenzo [Member] | Employee Severance [Member]                
Commitments And Contingencies [Line Items]                
General and administrative       $ 2,700,000        
Accounts payable, accrued expenses and other liabilities   $ 53,000       $ 53,000    
Time-Based Award [Member] | Messr Rudin [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Shares granted 32,311              
Time-Based Award [Member] | Messr Krug [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Accelerated vesting shares           13,306    
Time-Based Award [Member] | Messr DeLorenzo [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Partial accelerated vesting shares           9,111    
Performance Shares [Member] | Messr Rudin [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Shares granted 175,127              
Performance Shares [Member] | Messr Krug [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Accelerated vesting shares           18,665    
Performance Shares [Member] | Messr DeLorenzo [Member] | Mack-Cali Realty LP [Member]                
Commitments And Contingencies [Line Items]                
Partial accelerated vesting shares           13,982