Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies (Narrative) (Details)

v3.20.1
Significant Accounting Policies (Narrative) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Jan. 01, 2019
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2019
Dec. 31, 2017
Apr. 02, 2020
Jan. 03, 2020
Dec. 31, 2018
Significant Accounting Policies [Line Items]                
Capitalized development and construction salaries and other related costs   $ 500,000   $ 600,000        
Maximum period after cessation of major construction activity that projects are considered complete   1 year            
Threshold of investment value for discontinuation of equity method accounting   $ 0            
Amortization of deferred financing costs   1,024,000   1,189,000        
Leasing personnel costs   1,038,000   $ 742,000        
Deferred tax asset   10,100,000     $ 5,300,000      
Income taxes, material adjustment amount   $ 0            
Common stock, shares outstanding   90,596,079 90,595,176       90,595,197  
Common units outstanding   9,518,638 9,612,064 10,009,355     9,488,794 10,229,349
LTIP units outstanding   3,094,324 1,826,331 1,826,331     1,949,601 1,707,106
Distributions payable, record date   Apr. 02, 2020 Jan. 03, 2020          
Distributions payable, approved date   Mar. 23, 2020 Dec. 17, 2019          
Common stock dividends and common unit distributions per share   $ 0.20 $ 0.20          
Stock compensation expense   $ 2,530,000   $ 1,880,000        
Distributions payable, pay date   Apr. 14, 2020 Jan. 10, 2020          
Increase (decrease) to valuation allowance         $ (5,300,000)      
Federal income tax rate   21.00%            
Gain from extinguishment of debt, net       1,311,000        
Net income (loss)   $ (37,844,000)   275,594,000        
Accounting Standards Update 2017-12 [Member]                
Significant Accounting Policies [Line Items]                
Net income (loss) $ 400,000              
Subsequent Event [Member]                
Significant Accounting Policies [Line Items]                
Common stock, shares outstanding           90,596,168    
Common units outstanding           9,394,754    
LTIP units outstanding           3,218,208    
Mack-Cali Realty LP [Member]                
Significant Accounting Policies [Line Items]                
Gain from extinguishment of debt, net       1,311,000        
Net income (loss)   (37,844,000)   $ 275,594,000        
LTIP value     $ 400,000          
Dividends paid   400,000 18,100,000          
Mack-Cali Realty LP [Member] | General Partner Common Unitholders [Member]                
Significant Accounting Policies [Line Items]                
Dividends paid   18,100,000            
Common Units [Member] | Mack-Cali Realty LP [Member] | Limited Partner Common Unitholders [Member]                
Significant Accounting Policies [Line Items]                
Dividends paid   $ 1,900,000 $ 1,900,000