Recent Transactions (Unconsolidated Joint Venture Activity) (Narrative) (Details)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 03, 2017
USD ($)
shares
Jan. 31, 2017
USD ($)
May 26, 2016
USD ($)
item
Apr. 01, 2016
USD ($)
Oct. 31, 2016
Jun. 30, 2016
USD ($)
Mar. 31, 2016
Jun. 30, 2015
USD ($)
Dec. 31, 2016
USD ($)
item
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Real Estate Properties [Line Items]                      
Purchase price of property                 $ 121,582,000 $ 94,073,000 $ 91,813,000
Gain on sale of investment in unconsolidated joint venture           $ 5,670,000   $ 6,448,000 5,670,000 6,448,000  
Proceeds from the sale of investments in unconsolidated joint ventures                 $ 6,420,000 6,448,000  
Expiration period                 10 years    
Acquisition cost                 $ 35,930,000 78,027,000 67,325,000
Multi-Family Properties [Member]                      
Real Estate Properties [Line Items]                      
Number of units | item                 5,614    
Mack-Cali Realty LP [Member]                      
Real Estate Properties [Line Items]                      
Purchase price of property                 $ 121,582,000 94,073,000 91,813,000
Gain on sale of investment in unconsolidated joint venture           $ 5,670,000   $ 6,448,000 5,670,000 6,448,000  
Proceeds from the sale of investments in unconsolidated joint ventures                 6,420,000 6,448,000  
Acquisition cost                 $ 35,930,000 $ 78,027,000 $ 67,325,000
PruRose Riverwalk G, L.L.C. [Member]                      
Real Estate Properties [Line Items]                      
Purchase price of property       $ 11,300,000              
Percentage of additional interest acquired       50.00%     25.00%        
Number of units | item                 316    
Percent of pari passu interest         22.50%            
PruRose Port Imperial South 15, L.L.C. [Member]                      
Real Estate Properties [Line Items]                      
Number of units | item     236                
Percentage of interest in venture     50.00%                
PruRose Port Imperial South 13, L.L.C. [Member]                      
Real Estate Properties [Line Items]                      
Percentage of interest in venture     20.00%                
PruRose Port Imperial South 13, L.L.C. [Member] | Multi-Family Properties [Member]                      
Real Estate Properties [Line Items]                      
Number of units | item     280                
Pru Rose Port Imperial South 15 L.L.C. And Pru Rose Port Imperial South 13 L.L.C. [Member]                      
Real Estate Properties [Line Items]                      
Gain on sale of investment in unconsolidated joint venture     $ 5,700,000                
Proceeds from the sale of investments in unconsolidated joint ventures     $ 6,400,000                
Subsequent Event [Member]                      
Real Estate Properties [Line Items]                      
Percentage of additional interest acquired 12.50%                    
Percentage of interest in venture 100.00%                    
Acquisition cost $ 14,300,000                    
Subsequent Event [Member] | Mack-Cali Realty LP [Member] | Preferred Units [Member]                      
Real Estate Properties [Line Items]                      
Preferred units shares issued | shares 42,800                    
Preferred unit annual rate 3.50%                    
Percentage of interest in venture 37.50%                    
Preferred unit in operating partnership $ 1,000                    
Convertible preferred units | shares 28.15                    
Shares converted to common units | shares 1,204,820                    
Expiration period 5 years                    
Subsequent Event [Member] | KPG-P 100 IMW JV, LLC, Keystone-Penn And Keystone-Tristate [Member]                      
Real Estate Properties [Line Items]                      
Proceeds from the sale of investments in unconsolidated joint ventures   $ 9,700,000