Annual report pursuant to Section 13 and 15(d)

Recent Transactions (Unconsolidated Joint Venture Activity) (Narrative) (Details)

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Recent Transactions (Unconsolidated Joint Venture Activity) (Narrative) (Details) - USD ($)
12 Months Ended
Sep. 01, 2021
Apr. 29, 2021
Dec. 17, 2020
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Real Estate Properties [Line Items]            
Gain on sale from unconsolidated joint ventures       $ (1,886,000) $ 35,184,000 $ 903,000
Sale price $ 1,900,000          
Crystal House [Member]            
Real Estate Properties [Line Items]            
Gain on sale         $ 35,100,000  
Crystal House [Member] | Unconsolidated Joint Venture Office Buildings [Member]            
Real Estate Properties [Line Items]            
Gain on sale from unconsolidated joint ventures       376,600,000    
Gain on sale       35,100,000    
Gain (loss) on sale of property       62,700,000    
Hillsborough 206 [Member] | Unconsolidated Joint Venture Developable Land [Member]            
Real Estate Properties [Line Items]            
Gain on sale     $ 100,000      
Sale price     $ 2,100,000      
12 Vreeland Road [Member]            
Real Estate Properties [Line Items]            
Sale price   $ 2,000,000        
12 Vreeland Road [Member] | Unconsolidated Joint Venture Office Buildings [Member]            
Real Estate Properties [Line Items]            
Gain (loss) on sale of property   0        
Sale price   $ 2,000,000        
Offices At Crystal Lake [Member]            
Real Estate Properties [Line Items]            
Loss on Sale of Investments 1,900,000          
Sale price 1,900,000          
Offices At Crystal Lake [Member] | Unconsolidated Joint Venture Office Buildings [Member]            
Real Estate Properties [Line Items]            
Loss on Sale of Investments       $ (1,900,000)    
Sale price $ 1,900,000