Quarterly report pursuant to Section 13 or 15(d)

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

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Recent Transactions (Unconsolidated Joint Venture Activity) (Narrative) (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 01, 2021
Apr. 29, 2021
Sep. 30, 2021
Sep. 30, 2021
Dec. 31, 2020
Real Estate Properties [Line Items]          
Gain on sale from unconsolidated joint ventures     $ (1,886,000) $ (1,886,000)  
Crystal House [Member] | Unconsolidated Joint Venture Multi-Family Properties [Member]          
Real Estate Properties [Line Items]          
Gain on sale         $ 35,100,000
12 Vreeland Road [Member]          
Real Estate Properties [Line Items]          
Gain on sale from unconsolidated joint ventures   $ 0      
Gain on sale   2,000,000      
Sale price   $ 2,000,000      
Offices At Crystal Lake [Member]          
Real Estate Properties [Line Items]          
Gain on sale from unconsolidated joint ventures     $ (1,900,000) $ (1,900,000)  
Sale price $ 1,900,000        
Offices At Crystal Lake [Member] | Unconsolidated Joint Venture Office Buildings [Member]          
Real Estate Properties [Line Items]          
Gain on sale (1,900,000)        
Sale price $ 1,900,000