Real Estate Investments And Accumulated Depreciation (Schedule Of Real Estate Investments And Accumulated Depreciation) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Related Encumbrances $ 1,403,615      
Initial Costs, Land 789,095      
Initial Costs, Building and Improvements 3,553,425      
Costs Capitalized Subsequent to Acquisition [1] 760,324      
Gross Amount at Which Carried at Close of Period, Land [2] 786,789      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,316,055      
Total 5,102,844 [3] $ 4,804,867 $ 4,807,718 $ 4,958,179
Accumulated Depreciation 1,087,083 [4] $ 1,332,073 $ 1,464,482 $ 1,414,305
Real Estate Aggregate Cost, Tax Purpose $ 3,900,000      
Office [Member] | One Bridge Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1981      
Acquired 1996      
Initial Costs, Land $ 2,439      
Initial Costs, Building and Improvements 24,462      
Costs Capitalized Subsequent to Acquisition [1] 7,482      
Gross Amount at Which Carried at Close of Period, Land [2] 2,439      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 31,944      
Total [3] 34,383      
Accumulated Depreciation [4] $ 16,885      
Office [Member] | 2115 Linwood Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1981      
Acquired 1998      
Initial Costs, Land $ 474      
Initial Costs, Building and Improvements 4,419      
Costs Capitalized Subsequent to Acquisition [1] 7,756      
Gross Amount at Which Carried at Close of Period, Land [2] 474      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 12,175      
Total [3] 12,649      
Accumulated Depreciation [4] $ 5,035      
Office [Member] | 150 J.F. Kennedy Parkway [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1980      
Acquired 1997      
Initial Costs, Land $ 12,606      
Initial Costs, Building and Improvements 50,425      
Costs Capitalized Subsequent to Acquisition [1] 15,149      
Gross Amount at Which Carried at Close of Period, Land [2] 12,606      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 65,574      
Total [3] 78,180      
Accumulated Depreciation [4] $ 30,833      
Office [Member] | 75 Livingston Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1985      
Acquired 2009      
Related Encumbrances $ 4,478      
Initial Costs, Land 1,900      
Initial Costs, Building and Improvements 6,312      
Costs Capitalized Subsequent to Acquisition [1] (1,725)      
Gross Amount at Which Carried at Close of Period, Land [2] 1,281      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 5,206      
Total [3] 6,487      
Accumulated Depreciation [4] $ 1,387      
Office [Member] | 51 J.F. Kennedy Parkway [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1988      
Acquired 2017      
Related Encumbrances $ 69,393      
Initial Costs, Land 5,873      
Initial Costs, Building and Improvements 100,359      
Gross Amount at Which Carried at Close of Period, Land [2] 5,873      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 100,359      
Total [3] 106,232      
Accumulated Depreciation [4] $ 3,115      
Office [Member] | 101 J.F. Kennedy Parkway [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1981      
Acquired 2017      
Related Encumbrances $ 29,169      
Initial Costs, Land 4,380      
Initial Costs, Building and Improvements 59,730      
Gross Amount at Which Carried at Close of Period, Land [2] 4,380      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 59,730      
Total [3] 64,110      
Accumulated Depreciation [4] $ 1,844      
Office [Member] | 103 J.F. Kennedy Parkway [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1981      
Acquired 2017      
Related Encumbrances $ 24,852      
Initial Costs, Land 3,158      
Initial Costs, Building and Improvements 50,813      
Gross Amount at Which Carried at Close of Period, Land [2] 3,158      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 50,813      
Total [3] 53,971      
Accumulated Depreciation [4] $ 1,555      
Office [Member] | 111 River Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2002      
Acquired 2016      
Initial Costs, Land $ 204      
Initial Costs, Building and Improvements 198,609      
Costs Capitalized Subsequent to Acquisition [1] 14,771      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 213,584      
Total [3] 213,584      
Accumulated Depreciation [4] $ 8,680      
Office [Member] | Harborside Plaza 1 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 1996      
Initial Costs, Land $ 3,923      
Initial Costs, Building and Improvements 51,013      
Costs Capitalized Subsequent to Acquisition [1] 27,936      
Gross Amount at Which Carried at Close of Period, Land [2] 3,923      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 78,949      
Total [3] 82,872      
Accumulated Depreciation [4] $ 44,931      
Office [Member] | Harborside Plaza 2 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1996      
Initial Costs, Land $ 17,655      
Initial Costs, Building and Improvements 101,546      
Costs Capitalized Subsequent to Acquisition [1] 40,011      
Gross Amount at Which Carried at Close of Period, Land [2] 8,364      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 150,848      
Total [3] 159,212      
Accumulated Depreciation [4] $ 64,754      
Office [Member] | Harborside Plaza 3 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1996      
Initial Costs, Land $ 17,655      
Initial Costs, Building and Improvements 101,878      
Costs Capitalized Subsequent to Acquisition [1] 39,678      
Gross Amount at Which Carried at Close of Period, Land [2] 8,363      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 150,848      
Total [3] 159,211      
Accumulated Depreciation [4] $ 64,754      
Office [Member] | Harborside Plaza 4A [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2000      
Acquired 2000      
Initial Costs, Land $ 1,244      
Initial Costs, Building and Improvements 56,144      
Costs Capitalized Subsequent to Acquisition [1] 8,452      
Gross Amount at Which Carried at Close of Period, Land [2] 1,244      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 64,596      
Total [3] 65,840      
Accumulated Depreciation [4] $ 29,121      
Office [Member] | Harborside Plaza 5 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2002      
Acquired 2002      
Related Encumbrances $ 209,180      
Initial Costs, Land 6,218      
Initial Costs, Building and Improvements 170,682      
Costs Capitalized Subsequent to Acquisition [1] 61,569      
Gross Amount at Which Carried at Close of Period, Land [2] 5,705      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 232,764      
Total [3] 238,469      
Accumulated Depreciation [4] $ 98,606      
Office [Member] | 101 Hudson Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1992      
Acquired 2005      
Related Encumbrances $ 248,261      
Initial Costs, Land 45,530      
Initial Costs, Building and Improvements 271,376      
Costs Capitalized Subsequent to Acquisition [1] 16,952      
Gross Amount at Which Carried at Close of Period, Land [2] 45,530      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 288,328      
Total [3] 333,858      
Accumulated Depreciation [4] $ 93,337      
Office [Member] | 100 Avenue At Port Imperial [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2016      
Acquired 2016      
Initial Costs, Land $ 350      
Costs Capitalized Subsequent to Acquisition [1] 4,205      
Gross Amount at Which Carried at Close of Period, Land [2] 471      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,084      
Total [3] 4,555      
Accumulated Depreciation [4] $ 186      
Office [Member] | 500 Avenue At Port Imperial [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2013      
Acquired 2013      
Related Encumbrances $ 36,260      
Initial Costs, Land 13,099      
Initial Costs, Building and Improvements 56,669      
Costs Capitalized Subsequent to Acquisition [1] (20,540)      
Gross Amount at Which Carried at Close of Period, Land [2] 13,099      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 36,129      
Total [3] 49,228      
Accumulated Depreciation [4] $ 3,982      
Office [Member] | 700 Horizon Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2007      
Acquired 2007      
Initial Costs, Land $ 490      
Initial Costs, Building and Improvements 43      
Costs Capitalized Subsequent to Acquisition [1] 16,663      
Gross Amount at Which Carried at Close of Period, Land [2] 865      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 16,331      
Total [3] 17,196      
Accumulated Depreciation [4] $ 5,046      
Office [Member] | 100 Overlook Center [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1988      
Acquired 1997      
Initial Costs, Land $ 2,378      
Initial Costs, Building and Improvements 21,754      
Costs Capitalized Subsequent to Acquisition [1] 4,245      
Gross Amount at Which Carried at Close of Period, Land [2] 2,378      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 25,999      
Total [3] 28,377      
Accumulated Depreciation [4] $ 12,960      
Office [Member] | 5 Vaughn Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1995      
Initial Costs, Land $ 657      
Initial Costs, Building and Improvements 9,800      
Costs Capitalized Subsequent to Acquisition [1] 1,983      
Gross Amount at Which Carried at Close of Period, Land [2] 657      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 11,783      
Total [3] 12,440      
Accumulated Depreciation [4] $ 6,547      
Office [Member] | 333 Thornall Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1984      
Acquired 2015      
Initial Costs, Land $ 5,542      
Initial Costs, Building and Improvements 40,762      
Costs Capitalized Subsequent to Acquisition [1] 2,344      
Gross Amount at Which Carried at Close of Period, Land [2] 5,542      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 43,106      
Total [3] 48,648      
Accumulated Depreciation [4] $ 3,319      
Office [Member] | 343 Thornall Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1991      
Acquired 2006      
Initial Costs, Land $ 6,027      
Initial Costs, Building and Improvements 39,101      
Costs Capitalized Subsequent to Acquisition [1] 11,532      
Gross Amount at Which Carried at Close of Period, Land [2] 6,027      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 50,633      
Total [3] 56,660      
Accumulated Depreciation [4] $ 14,840      
Office [Member] | 101 Wood Avenue South [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 2016      
Initial Costs, Land $ 8,509      
Initial Costs, Building and Improvements 72,738      
Costs Capitalized Subsequent to Acquisition [1] 692      
Gross Amount at Which Carried at Close of Period, Land [2] 7,384      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 74,555      
Total [3] 81,939      
Accumulated Depreciation [4] $ 4,315      
Office [Member] | 500 College Road East [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1984      
Acquired [5] 1998      
Initial Costs, Land [5] $ 614      
Initial Costs, Building and Improvements [5] 20,626      
Costs Capitalized Subsequent to Acquisition [1],[5] 5,708      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 614      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 26,334      
Total [3],[5] 26,948      
Accumulated Depreciation [4],[5] $ 13,152      
Office [Member] | 581 Main Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1991      
Acquired 1997      
Initial Costs, Land $ 3,237      
Initial Costs, Building and Improvements 12,949      
Costs Capitalized Subsequent to Acquisition [1] 24,191      
Gross Amount at Which Carried at Close of Period, Land [2] 8,115      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 32,262      
Total [3] 40,377      
Accumulated Depreciation [4] $ 15,056      
Office [Member] | 23 Main Street [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1977      
Acquired 2005      
Related Encumbrances $ 27,078      
Initial Costs, Land 4,336      
Initial Costs, Building and Improvements 19,544      
Costs Capitalized Subsequent to Acquisition [1] 13,944      
Gross Amount at Which Carried at Close of Period, Land [2] 4,336      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 33,488      
Total [3] 37,824      
Accumulated Depreciation [4] $ 15,515      
Office [Member] | One River Center, Building 1 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 2004      
Related Encumbrances $ 10,362      
Initial Costs, Land 3,070      
Initial Costs, Building and Improvements 17,414      
Costs Capitalized Subsequent to Acquisition [1] 11,421      
Gross Amount at Which Carried at Close of Period, Land [2] 2,451      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 29,454      
Total [3] 31,905      
Accumulated Depreciation [4] $ 9,154      
Office [Member] | One River Center, Building 2 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 2004      
Related Encumbrances $ 11,624      
Initial Costs, Land 2,468      
Initial Costs, Building and Improvements 15,043      
Costs Capitalized Subsequent to Acquisition [1] 4,101      
Gross Amount at Which Carried at Close of Period, Land [2] 2,452      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 19,160      
Total [3] 21,612      
Accumulated Depreciation [4] $ 7,093      
Office [Member] | One River Center, Building 3 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1984      
Acquired 2004      
Related Encumbrances $ 18,472      
Initial Costs, Land 4,051      
Initial Costs, Building and Improvements 24,790      
Costs Capitalized Subsequent to Acquisition [1] 5,687      
Gross Amount at Which Carried at Close of Period, Land [2] 4,627      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 29,901      
Total [3] 34,528      
Accumulated Depreciation [4] $ 10,588      
Office [Member] | 3600 Route 66 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 1995      
Initial Costs, Land $ 1,098      
Initial Costs, Building and Improvements 18,146      
Costs Capitalized Subsequent to Acquisition [1] 11,471      
Gross Amount at Which Carried at Close of Period, Land [2] 1,098      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 29,617      
Total [3] 30,715      
Accumulated Depreciation [4] $ 14,193      
Office [Member] | 100 Schultz Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 2017      
Costs Capitalized Subsequent to Acquisition [1] $ 8,743      
Gross Amount at Which Carried at Close of Period, Land [2] 1,953      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 6,790      
Total [3] 8,743      
Accumulated Depreciation [4] $ 556      
Office [Member] | 200 Schultz Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 2017      
Costs Capitalized Subsequent to Acquisition [1] $ 10,443      
Gross Amount at Which Carried at Close of Period, Land [2] 2,184      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,259      
Total [3] 10,443      
Accumulated Depreciation [4] $ 495      
Office [Member] | 325 Columbia Parkway [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1994      
Initial Costs, Land $ 1,564      
Costs Capitalized Subsequent to Acquisition [1] 18,368      
Gross Amount at Which Carried at Close of Period, Land [2] 1,564      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 18,368      
Total [3] 19,932      
Accumulated Depreciation [4] $ 12,583      
Office [Member] | 1 Giralda Farms [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1982      
Acquired 2017      
Costs Capitalized Subsequent to Acquisition [1] $ 30,515      
Gross Amount at Which Carried at Close of Period, Land [2] 3,370      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 27,145      
Total [3] 30,515      
Accumulated Depreciation [4] $ 1,014      
Office [Member] | 7 Giralda Farms [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1997      
Acquired 2017      
Costs Capitalized Subsequent to Acquisition [1] $ 43,066      
Gross Amount at Which Carried at Close of Period, Land [2] 5,402      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 37,664      
Total [3] 43,066      
Accumulated Depreciation [4] $ 1,246      
Office [Member] | 201 Littleton Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1979      
Acquired 1997      
Initial Costs, Land $ 2,407      
Initial Costs, Building and Improvements 9,627      
Costs Capitalized Subsequent to Acquisition [1] 3,132      
Gross Amount at Which Carried at Close of Period, Land [2] 2,407      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 12,759      
Total [3] 15,166      
Accumulated Depreciation [4] $ 6,416      
Office [Member] | 4 Campus Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 2001      
Initial Costs, Land $ 5,213      
Initial Costs, Building and Improvements 20,984      
Costs Capitalized Subsequent to Acquisition [1] 4,117      
Gross Amount at Which Carried at Close of Period, Land [2] 5,213      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 25,101      
Total [3] 30,314      
Accumulated Depreciation [4] $ 10,513      
Office [Member] | 6 Campus Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 2001      
Initial Costs, Land $ 4,411      
Initial Costs, Building and Improvements 17,796      
Costs Capitalized Subsequent to Acquisition [1] 3,550      
Gross Amount at Which Carried at Close of Period, Land [2] 4,411      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 21,346      
Total [3] 25,757      
Accumulated Depreciation [4] $ 9,177      
Office [Member] | 7 Campus Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1982      
Acquired 1998      
Initial Costs, Land $ 1,932      
Initial Costs, Building and Improvements 27,788      
Costs Capitalized Subsequent to Acquisition [1] 6,573      
Gross Amount at Which Carried at Close of Period, Land [2] 1,932      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 34,361      
Total [3] 36,293      
Accumulated Depreciation [4] $ 17,234      
Office [Member] | 8 Campus Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1998      
Initial Costs, Land $ 1,865      
Initial Costs, Building and Improvements 35,456      
Costs Capitalized Subsequent to Acquisition [1] 11,139      
Gross Amount at Which Carried at Close of Period, Land [2] 1,865      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 46,595      
Total [3] 48,460      
Accumulated Depreciation [4] $ 20,169      
Office [Member] | 9 Campus Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 2001      
Initial Costs, Land $ 3,277      
Initial Costs, Building and Improvements 11,796      
Costs Capitalized Subsequent to Acquisition [1] 22,609      
Gross Amount at Which Carried at Close of Period, Land [2] 5,842      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 31,840      
Total [3] 37,682      
Accumulated Depreciation [4] $ 12,352      
Office [Member] | 2 Dryden Way [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1998      
Initial Costs, Land $ 778      
Initial Costs, Building and Improvements 420      
Costs Capitalized Subsequent to Acquisition [1] 110      
Gross Amount at Which Carried at Close of Period, Land [2] 778      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 530      
Total [3] 1,308      
Accumulated Depreciation [4] $ 302      
Office [Member] | 4 Gatehall Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1988      
Acquired 2000      
Initial Costs, Land $ 8,452      
Initial Costs, Building and Improvements 33,929      
Costs Capitalized Subsequent to Acquisition [1] 5,302      
Gross Amount at Which Carried at Close of Period, Land [2] 8,452      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 39,231      
Total [3] 47,683      
Accumulated Depreciation [4] $ 17,628      
Office [Member] | 2 Hilton Court [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1991      
Acquired 1998      
Initial Costs, Land $ 1,971      
Initial Costs, Building and Improvements 32,007      
Costs Capitalized Subsequent to Acquisition [1] 4,474      
Gross Amount at Which Carried at Close of Period, Land [2] 1,971      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 36,481      
Total [3] 38,452      
Accumulated Depreciation [4] $ 18,874      
Office [Member] | 1 Sylvan Way [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 1998      
Initial Costs, Land $ 1,689      
Initial Costs, Building and Improvements 24,699      
Costs Capitalized Subsequent to Acquisition [1] 2,253      
Gross Amount at Which Carried at Close of Period, Land [2] 1,021      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 27,620      
Total [3] 28,641      
Accumulated Depreciation [4] $ 13,301      
Office [Member] | 3 Sylvan Way [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1988      
Acquired 2015      
Initial Costs, Land $ 5,590      
Initial Costs, Building and Improvements 4,710      
Costs Capitalized Subsequent to Acquisition [1] 4,033      
Gross Amount at Which Carried at Close of Period, Land [2] 5,590      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,743      
Total [3] 14,333      
Accumulated Depreciation [4] $ 280      
Office [Member] | 5 Sylvan Way [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 1998      
Initial Costs, Land $ 1,160      
Initial Costs, Building and Improvements 25,214      
Costs Capitalized Subsequent to Acquisition [1] 4,769      
Gross Amount at Which Carried at Close of Period, Land [2] 1,161      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 29,982      
Total [3] 31,143      
Accumulated Depreciation [4] $ 13,950      
Office [Member] | 7 Sylvan Way [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1998      
Initial Costs, Land $ 2,084      
Initial Costs, Building and Improvements 26,083      
Costs Capitalized Subsequent to Acquisition [1] 14,805      
Gross Amount at Which Carried at Close of Period, Land [2] 2,084      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 40,888      
Total [3] 42,972      
Accumulated Depreciation [4] $ 14,057      
Office [Member] | 5 Wood Hollow Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1979      
Acquired 2004      
Initial Costs, Land $ 5,302      
Initial Costs, Building and Improvements 26,488      
Costs Capitalized Subsequent to Acquisition [1] 20,963      
Gross Amount at Which Carried at Close of Period, Land [2] 5,302      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 47,451      
Total [3] 52,753      
Accumulated Depreciation [4] $ 19,473      
Office [Member] | 721 Route 202/206 [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1989      
Acquired 1997      
Initial Costs, Land $ 6,730      
Initial Costs, Building and Improvements 26,919      
Costs Capitalized Subsequent to Acquisition [1] (5,309)      
Gross Amount at Which Carried at Close of Period, Land [2] 5,067      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 23,273      
Total [3] 28,340      
Accumulated Depreciation [4] $ 12,109      
Office [Member] | 100 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1975      
Acquired 1997      
Initial Costs, Land $ 220      
Initial Costs, Building and Improvements 5,366      
Costs Capitalized Subsequent to Acquisition [1] 1,674      
Gross Amount at Which Carried at Close of Period, Land [2] 220      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 7,040      
Total [3] 7,260      
Accumulated Depreciation [4] $ 3,422      
Office [Member] | 101 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1971      
Acquired 1997      
Initial Costs, Land $ 267      
Initial Costs, Building and Improvements 5,838      
Costs Capitalized Subsequent to Acquisition [1] (6,004)      
Gross Amount at Which Carried at Close of Period, Land [2] 101      
Total [3] $ 101      
Office [Member] | 1 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1980      
Acquired 1997      
Initial Costs, Land $ 66      
Initial Costs, Building and Improvements 1,711      
Costs Capitalized Subsequent to Acquisition [1] 210      
Gross Amount at Which Carried at Close of Period, Land [2] 66      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 1,921      
Total [3] 1,987      
Accumulated Depreciation [4] $ 1,049      
Office [Member] | 2 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1997      
Initial Costs, Land $ 109      
Initial Costs, Building and Improvements 3,128      
Costs Capitalized Subsequent to Acquisition [1] 1,474      
Gross Amount at Which Carried at Close of Period, Land [2] 109      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,602      
Total [3] 4,711      
Accumulated Depreciation [4] $ 2,696      
Office [Member] | 7 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1998      
Initial Costs, Land $ 330      
Initial Costs, Building and Improvements 13,013      
Costs Capitalized Subsequent to Acquisition [1] 2,929      
Gross Amount at Which Carried at Close of Period, Land [2] 330      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 15,942      
Total [3] 16,272      
Accumulated Depreciation [4] $ 7,758      
Office [Member] | 17 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1989      
Acquired [5] 1997      
Initial Costs, Building and Improvements [5] $ 7,269      
Costs Capitalized Subsequent to Acquisition [1],[5] 1,484      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 8,753      
Total [3],[5] 8,753      
Accumulated Depreciation [4],[5] $ 4,540      
Office [Member] | 1 Barker Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1975      
Acquired 1997      
Initial Costs, Land $ 208      
Initial Costs, Building and Improvements 9,629      
Costs Capitalized Subsequent to Acquisition [1] 3,248      
Gross Amount at Which Carried at Close of Period, Land [2] 207      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 12,878      
Total [3] 13,085      
Accumulated Depreciation [4] $ 6,406      
Office [Member] | 3 Barker Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 1997      
Initial Costs, Land $ 122      
Initial Costs, Building and Improvements 7,864      
Costs Capitalized Subsequent to Acquisition [1] 2,117      
Gross Amount at Which Carried at Close of Period, Land [2] 122      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,981      
Total [3] 10,103      
Accumulated Depreciation [4] $ 5,076      
Office [Member] | 1 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1982      
Acquired 1997      
Initial Costs, Land $ 1,104      
Initial Costs, Building and Improvements 11,904      
Costs Capitalized Subsequent to Acquisition [1] 3,815      
Gross Amount at Which Carried at Close of Period, Land [2] 1,105      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 15,718      
Total [3] 16,823      
Accumulated Depreciation [4] $ 7,750      
Office [Member] | 3 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1997      
Initial Costs, Land $ 385      
Initial Costs, Building and Improvements 6,256      
Costs Capitalized Subsequent to Acquisition [1] 1,817      
Gross Amount at Which Carried at Close of Period, Land [2] 385      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,073      
Total [3] 8,458      
Accumulated Depreciation [4] $ 4,219      
Office [Member] | 3 Odell Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1984      
Acquired 2003      
Initial Costs, Land $ 1,322      
Initial Costs, Building and Improvements 4,777      
Costs Capitalized Subsequent to Acquisition [1] 2,332      
Gross Amount at Which Carried at Close of Period, Land [2] 1,322      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 7,109      
Total [3] 8,431      
Accumulated Depreciation [4] $ 3,736      
Office And Office/Flex Buildings [Member] | 600 Horizon Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2002      
Acquired 2002      
Initial Costs, Building and Improvements $ 7,549      
Costs Capitalized Subsequent to Acquisition [1] 1,189      
Gross Amount at Which Carried at Close of Period, Land [2] 685      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,053      
Total [3] 8,738      
Accumulated Depreciation [4] $ 3,218      
Office And Office/Flex Buildings [Member] | 11 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1974      
Acquired 1997      
Initial Costs, Land $ 149      
Initial Costs, Building and Improvements 2,159      
Costs Capitalized Subsequent to Acquisition [1] 578      
Gross Amount at Which Carried at Close of Period, Land [2] 149      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,737      
Total [3] 2,886      
Accumulated Depreciation [4] $ 1,452      
Office And Office/Flex Buildings [Member] | 75 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1997      
Initial Costs, Land $ 2,314      
Initial Costs, Building and Improvements 4,716      
Costs Capitalized Subsequent to Acquisition [1] 57      
Gross Amount at Which Carried at Close of Period, Land [2] 2,314      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,773      
Total [3] 7,087      
Accumulated Depreciation [4] $ 2,500      
Office And Office/Flex Buildings [Member] | 125 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2002      
Acquired 2002      
Initial Costs, Land $ 1,055      
Initial Costs, Building and Improvements 3,676      
Costs Capitalized Subsequent to Acquisition [1] (252)      
Gross Amount at Which Carried at Close of Period, Land [2] 1,055      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,424      
Total [3] 4,479      
Accumulated Depreciation [4] $ 1,500      
Office And Office/Flex Buildings [Member] | 150 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1975      
Acquired 1997      
Initial Costs, Land $ 497      
Initial Costs, Building and Improvements 7,030      
Costs Capitalized Subsequent to Acquisition [1] 2,156      
Gross Amount at Which Carried at Close of Period, Land [2] 497      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,186      
Total [3] 9,683      
Accumulated Depreciation [4] $ 4,616      
Office And Office/Flex Buildings [Member] | 175 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1973      
Acquired 1997      
Initial Costs, Land $ 655      
Initial Costs, Building and Improvements 7,473      
Costs Capitalized Subsequent to Acquisition [1] 953      
Gross Amount at Which Carried at Close of Period, Land [2] 655      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,426      
Total [3] 9,081      
Accumulated Depreciation [4] $ 4,444      
Office And Office/Flex Buildings [Member] | 200 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1974      
Acquired 1997      
Initial Costs, Land $ 579      
Initial Costs, Building and Improvements 6,620      
Costs Capitalized Subsequent to Acquisition [1] 1,667      
Gross Amount at Which Carried at Close of Period, Land [2] 579      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 8,287      
Total [3] 8,866      
Accumulated Depreciation [4] $ 4,066      
Office And Office/Flex Buildings [Member] | 250 Clearbrook Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1973      
Acquired 1997      
Initial Costs, Land $ 867      
Initial Costs, Building and Improvements 8,647      
Costs Capitalized Subsequent to Acquisition [1] 2,434      
Gross Amount at Which Carried at Close of Period, Land [2] 867      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 11,081      
Total [3] 11,948      
Accumulated Depreciation [4] $ 5,458      
Office And Office/Flex Buildings [Member] | 50 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1969      
Acquired 1997      
Initial Costs, Land $ 237      
Initial Costs, Building and Improvements 2,617      
Costs Capitalized Subsequent to Acquisition [1] 540      
Gross Amount at Which Carried at Close of Period, Land [2] 237      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,157      
Total [3] 3,394      
Accumulated Depreciation [4] $ 1,620      
Office And Office/Flex Buildings [Member] | 77 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1977      
Acquired 1997      
Initial Costs, Land $ 34      
Initial Costs, Building and Improvements 1,104      
Costs Capitalized Subsequent to Acquisition [1] 177      
Gross Amount at Which Carried at Close of Period, Land [2] 34      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 1,281      
Total [3] 1,315      
Accumulated Depreciation [4] $ 695      
Office And Office/Flex Buildings [Member] | 85 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1968      
Acquired 1997      
Initial Costs, Land $ 155      
Initial Costs, Building and Improvements 2,507      
Costs Capitalized Subsequent to Acquisition [1] 538      
Gross Amount at Which Carried at Close of Period, Land [2] 155      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,045      
Total [3] 3,200      
Accumulated Depreciation [4] $ 1,560      
Office And Office/Flex Buildings [Member] | 300 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1970      
Acquired 1997      
Initial Costs, Land $ 460      
Initial Costs, Building and Improvements 3,609      
Costs Capitalized Subsequent to Acquisition [1] 302      
Gross Amount at Which Carried at Close of Period, Land [2] 460      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,911      
Total [3] 4,371      
Accumulated Depreciation [4] $ 2,015      
Office And Office/Flex Buildings [Member] | 350 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1970      
Acquired 1997      
Initial Costs, Land $ 100      
Initial Costs, Building and Improvements 1,793      
Costs Capitalized Subsequent to Acquisition [1] 175      
Gross Amount at Which Carried at Close of Period, Land [2] 100      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 1,968      
Total [3] 2,068      
Accumulated Depreciation [4] $ 1,085      
Office And Office/Flex Buildings [Member] | 399 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1962      
Acquired 1997      
Initial Costs, Land $ 531      
Initial Costs, Building and Improvements 7,191      
Costs Capitalized Subsequent to Acquisition [1] 163      
Gross Amount at Which Carried at Close of Period, Land [2] 531      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 7,354      
Total [3] 7,885      
Accumulated Depreciation [4] $ 3,885      
Office And Office/Flex Buildings [Member] | 400 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1970      
Acquired 1997      
Initial Costs, Land $ 2,202      
Initial Costs, Building and Improvements 1,846      
Costs Capitalized Subsequent to Acquisition [1] 1,140      
Gross Amount at Which Carried at Close of Period, Land [2] 2,202      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,986      
Total [3] 5,188      
Accumulated Depreciation [4] $ 1,662      
Office And Office/Flex Buildings [Member] | 500 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1970      
Acquired 1997      
Initial Costs, Land $ 258      
Initial Costs, Building and Improvements 4,183      
Costs Capitalized Subsequent to Acquisition [1] 384      
Gross Amount at Which Carried at Close of Period, Land [2] 258      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,567      
Total [3] 4,825      
Accumulated Depreciation [4] $ 2,514      
Office And Office/Flex Buildings [Member] | 525 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1972      
Acquired 1997      
Initial Costs, Land $ 345      
Initial Costs, Building and Improvements 5,499      
Costs Capitalized Subsequent to Acquisition [1] 900      
Gross Amount at Which Carried at Close of Period, Land [2] 345      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 6,399      
Total [3] 6,744      
Accumulated Depreciation [4] $ 3,520      
Office And Office/Flex Buildings [Member] | 1 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1967      
Acquired 1997      
Initial Costs, Land $ 199      
Initial Costs, Building and Improvements 2,023      
Costs Capitalized Subsequent to Acquisition [1] 152      
Gross Amount at Which Carried at Close of Period, Land [2] 199      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,175      
Total [3] 2,374      
Accumulated Depreciation [4] $ 1,156      
Office And Office/Flex Buildings [Member] | 2 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1968      
Acquired 1997      
Initial Costs, Land $ 234      
Initial Costs, Building and Improvements 2,726      
Costs Capitalized Subsequent to Acquisition [1] 914      
Gross Amount at Which Carried at Close of Period, Land [2] 234      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,640      
Total [3] 3,874      
Accumulated Depreciation [4] $ 1,806      
Office And Office/Flex Buildings [Member] | 3 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1969      
Acquired 1997      
Initial Costs, Land $ 655      
Initial Costs, Building and Improvements 7,936      
Costs Capitalized Subsequent to Acquisition [1] 1,407      
Gross Amount at Which Carried at Close of Period, Land [2] 655      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,343      
Total [3] 9,998      
Accumulated Depreciation [4] $ 4,541      
Office And Office/Flex Buildings [Member] | 4 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1969      
Acquired 1997      
Initial Costs, Land $ 320      
Initial Costs, Building and Improvements 3,729      
Costs Capitalized Subsequent to Acquisition [1] 1,979      
Gross Amount at Which Carried at Close of Period, Land [2] 320      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 5,708      
Total [3] 6,028      
Accumulated Depreciation [4] $ 2,825      
Office And Office/Flex Buildings [Member] | 5 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1969      
Acquired 1997      
Initial Costs, Land $ 118      
Initial Costs, Building and Improvements 1,949      
Costs Capitalized Subsequent to Acquisition [1] 374      
Gross Amount at Which Carried at Close of Period, Land [2] 118      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,323      
Total [3] 2,441      
Accumulated Depreciation [4] $ 1,247      
Office And Office/Flex Buildings [Member] | 6 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1968      
Acquired 1997      
Initial Costs, Land $ 164      
Initial Costs, Building and Improvements 1,998      
Costs Capitalized Subsequent to Acquisition [1] 160      
Gross Amount at Which Carried at Close of Period, Land [2] 164      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,158      
Total [3] 2,322      
Accumulated Depreciation [4] $ 1,124      
Office And Office/Flex Buildings [Member] | 7 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1972      
Acquired 1997      
Initial Costs, Land $ 286      
Initial Costs, Building and Improvements 4,321      
Costs Capitalized Subsequent to Acquisition [1] 1,166      
Gross Amount at Which Carried at Close of Period, Land [2] 286      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 5,487      
Total [3] 5,773      
Accumulated Depreciation [4] $ 2,575      
Office And Office/Flex Buildings [Member] | 8 Westchester Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1971      
Acquired 1997      
Initial Costs, Land $ 447      
Initial Costs, Building and Improvements 5,262      
Costs Capitalized Subsequent to Acquisition [1] 2,127      
Gross Amount at Which Carried at Close of Period, Land [2] 447      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 7,389      
Total [3] 7,836      
Accumulated Depreciation [4] $ 3,709      
Office And Office/Flex Buildings [Member] | 200 Saw Mill River Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1965      
Acquired 1997      
Initial Costs, Land $ 353      
Initial Costs, Building and Improvements 3,353      
Costs Capitalized Subsequent to Acquisition [1] 745      
Gross Amount at Which Carried at Close of Period, Land [2] 353      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,098      
Total [3] 4,451      
Accumulated Depreciation [4] $ 2,037      
Office And Office/Flex Buildings [Member] | 4 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1997      
Initial Costs, Land $ 363      
Initial Costs, Building and Improvements 7,513      
Costs Capitalized Subsequent to Acquisition [1] 3,071      
Gross Amount at Which Carried at Close of Period, Land [2] 363      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 10,584      
Total [3] 10,947      
Accumulated Depreciation [4] $ 6,190      
Office And Office/Flex Buildings [Member] | 5 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1980      
Acquired 2001      
Initial Costs, Land $ 2,219      
Initial Costs, Building and Improvements 8,916      
Costs Capitalized Subsequent to Acquisition [1] 1,841      
Gross Amount at Which Carried at Close of Period, Land [2] 2,219      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 10,757      
Total [3] 12,976      
Accumulated Depreciation [4] $ 5,495      
Office And Office/Flex Buildings [Member] | 6 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1980      
Acquired 2001      
Initial Costs, Land $ 740      
Initial Costs, Building and Improvements 2,971      
Costs Capitalized Subsequent to Acquisition [1] 1,295      
Gross Amount at Which Carried at Close of Period, Land [2] 740      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 4,266      
Total [3] 5,006      
Accumulated Depreciation [4] $ 2,582      
Office And Office/Flex Buildings [Member] | 8 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1985      
Acquired 1997      
Initial Costs, Land $ 212      
Initial Costs, Building and Improvements 4,410      
Costs Capitalized Subsequent to Acquisition [1] 777      
Gross Amount at Which Carried at Close of Period, Land [2] 212      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 5,187      
Total [3] 5,399      
Accumulated Depreciation [4] $ 2,893      
Office And Office/Flex Buildings [Member] | 10 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1985      
Acquired 1997      
Initial Costs, Land $ 134      
Initial Costs, Building and Improvements 2,799      
Costs Capitalized Subsequent to Acquisition [1] 812      
Gross Amount at Which Carried at Close of Period, Land [2] 134      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,611      
Total [3] 3,745      
Accumulated Depreciation [4] $ 2,121      
Office And Office/Flex Buildings [Member] | 11 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1989      
Acquired [5] 1997      
Initial Costs, Building and Improvements [5] $ 4,788      
Costs Capitalized Subsequent to Acquisition [1],[5] 763      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 5,551      
Total [3],[5] 5,551      
Accumulated Depreciation [4],[5] $ 2,741      
Office And Office/Flex Buildings [Member] | 12 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1999      
Acquired [5] 1999      
Initial Costs, Land [5] $ 1,562      
Initial Costs, Building and Improvements [5] 3,254      
Costs Capitalized Subsequent to Acquisition [1],[5] 218      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 1,320      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 3,714      
Total [3],[5] 5,034      
Accumulated Depreciation [4],[5] $ 1,790      
Office And Office/Flex Buildings [Member] | 15 Skyline Drive [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1989      
Acquired [5] 1997      
Initial Costs, Building and Improvements [5] $ 7,449      
Costs Capitalized Subsequent to Acquisition [1],[5] 1,749      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 9,198      
Total [3],[5] 9,198      
Accumulated Depreciation [4],[5] $ 4,220      
Office And Office/Flex Buildings [Member] | 100 Corporate Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1997      
Initial Costs, Land $ 602      
Initial Costs, Building and Improvements 9,910      
Costs Capitalized Subsequent to Acquisition [1] 1,334      
Gross Amount at Which Carried at Close of Period, Land [2] 602      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 11,244      
Total [3] 11,846      
Accumulated Depreciation [4] $ 5,973      
Office And Office/Flex Buildings [Member] | 200 Corporate Boulevard South [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1997      
Initial Costs, Land $ 502      
Initial Costs, Building and Improvements 7,575      
Costs Capitalized Subsequent to Acquisition [1] 3,116      
Gross Amount at Which Carried at Close of Period, Land [2] 502      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 10,691      
Total [3] 11,193      
Accumulated Depreciation [4] $ 5,159      
Office And Office/Flex Buildings [Member] | 4 Executive Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1986      
Acquired 1997      
Initial Costs, Land $ 584      
Initial Costs, Building and Improvements 6,134      
Costs Capitalized Subsequent to Acquisition [1] 995      
Gross Amount at Which Carried at Close of Period, Land [2] 584      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 7,129      
Total [3] 7,713      
Accumulated Depreciation [4] $ 3,664      
Office And Office/Flex Buildings [Member] | 6 Executive Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1987      
Acquired 1997      
Initial Costs, Land $ 546      
Initial Costs, Building and Improvements 7,246      
Costs Capitalized Subsequent to Acquisition [1] 2,360      
Gross Amount at Which Carried at Close of Period, Land [2] 546      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,606      
Total [3] 10,152      
Accumulated Depreciation [4] $ 4,942      
Office And Office/Flex Buildings [Member] | 1 Odell Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1980      
Acquired 1997      
Initial Costs, Land $ 1,206      
Initial Costs, Building and Improvements 6,815      
Costs Capitalized Subsequent to Acquisition [1] 2,367      
Gross Amount at Which Carried at Close of Period, Land [2] 1,206      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,182      
Total [3] 10,388      
Accumulated Depreciation [4] $ 4,775      
Office And Office/Flex Buildings [Member] | 5 Odell Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1983      
Acquired 1997      
Initial Costs, Land $ 331      
Initial Costs, Building and Improvements 2,988      
Costs Capitalized Subsequent to Acquisition [1] 535      
Gross Amount at Which Carried at Close of Period, Land [2] 331      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,523      
Total [3] 3,854      
Accumulated Depreciation [4] $ 1,990      
Office And Office/Flex Buildings [Member] | 7 Odell Plaza [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1984      
Acquired 1997      
Initial Costs, Land $ 419      
Initial Costs, Building and Improvements 4,418      
Costs Capitalized Subsequent to Acquisition [1] 1,366      
Gross Amount at Which Carried at Close of Period, Land [2] 419      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 5,784      
Total [3] 6,203      
Accumulated Depreciation [4] $ 2,886      
Office And Office/Flex Buildings [Member] | 419 West Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1986      
Acquired 1997      
Initial Costs, Land $ 4,538      
Initial Costs, Building and Improvements 9,246      
Costs Capitalized Subsequent to Acquisition [1] 482      
Gross Amount at Which Carried at Close of Period, Land [2] 4,538      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 9,728      
Total [3] 14,266      
Accumulated Depreciation [4] $ 5,060      
Office And Office/Flex Buildings [Member] | 500 West Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1988      
Acquired 1997      
Initial Costs, Land $ 415      
Initial Costs, Building and Improvements 1,679      
Costs Capitalized Subsequent to Acquisition [1] 646      
Gross Amount at Which Carried at Close of Period, Land [2] 415      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,325      
Total [3] 2,740      
Accumulated Depreciation [4] $ 1,098      
Office And Office/Flex Buildings [Member] | 550 West Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1990      
Acquired 1997      
Initial Costs, Land $ 1,975      
Initial Costs, Building and Improvements 3,856      
Costs Capitalized Subsequent to Acquisition [1] 133      
Gross Amount at Which Carried at Close of Period, Land [2] 1,975      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,989      
Total [3] 5,964      
Accumulated Depreciation [4] $ 2,065      
Office And Office/Flex Buildings [Member] | 600 West Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1999      
Acquired 1999      
Initial Costs, Land $ 2,305      
Initial Costs, Building and Improvements 2,863      
Costs Capitalized Subsequent to Acquisition [1] 1,005      
Gross Amount at Which Carried at Close of Period, Land [2] 2,305      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,868      
Total [3] 6,173      
Accumulated Depreciation [4] $ 1,611      
Office And Office/Flex Buildings [Member] | 650 West Avenue [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1998      
Acquired 1998      
Initial Costs, Land $ 1,328      
Costs Capitalized Subsequent to Acquisition [1] 3,268      
Gross Amount at Which Carried at Close of Period, Land [2] 1,328      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 3,268      
Total [3] 4,596      
Accumulated Depreciation [4] $ 1,613      
Industrial/Warehouse Facilities [Member] | 1 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1957      
Acquired [5] 1997      
Initial Costs, Land [5] $ 3      
Initial Costs, Building and Improvements [5] 268      
Costs Capitalized Subsequent to Acquisition [1],[5] 208      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 3      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 476      
Total [3],[5] 479      
Accumulated Depreciation [4],[5] $ 240      
Industrial/Warehouse Facilities [Member] | 2 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1957      
Acquired [5] 1997      
Initial Costs, Land [5] $ 4      
Initial Costs, Building and Improvements [5] 672      
Costs Capitalized Subsequent to Acquisition [1],[5] 341      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 4      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 1,013      
Total [3],[5] 1,017      
Accumulated Depreciation [4],[5] $ 444      
Industrial/Warehouse Facilities [Member] | 3 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1957      
Acquired [5] 1997      
Initial Costs, Land [5] $ 21      
Initial Costs, Building and Improvements [5] 1,948      
Costs Capitalized Subsequent to Acquisition [1],[5] 363      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 21      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 2,311      
Total [3],[5] 2,332      
Accumulated Depreciation [4],[5] $ 1,314      
Industrial/Warehouse Facilities [Member] | 4 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1957      
Acquired [5] 1997      
Initial Costs, Land [5] $ 84      
Initial Costs, Building and Improvements [5] 13,393      
Costs Capitalized Subsequent to Acquisition [1],[5] 3,665      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 85      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 17,057      
Total [3],[5] 17,142      
Accumulated Depreciation [4],[5] $ 8,441      
Industrial/Warehouse Facilities [Member] | 5 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1957      
Acquired [5] 1997      
Initial Costs, Land [5] $ 19      
Initial Costs, Building and Improvements [5] 4,804      
Costs Capitalized Subsequent to Acquisition [1],[5] 884      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 19      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 5,688      
Total [3],[5] 5,707      
Accumulated Depreciation [4],[5] $ 3,053      
Industrial/Warehouse Facilities [Member] | 6 Warehouse Lane [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built [5] 1982      
Acquired [5] 1997      
Initial Costs, Land [5] $ 10      
Initial Costs, Building and Improvements [5] 4,419      
Costs Capitalized Subsequent to Acquisition [1],[5] 2,381      
Gross Amount at Which Carried at Close of Period, Land [2],[5] 10      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2],[5] 6,800      
Total [3],[5] 6,810      
Accumulated Depreciation [4],[5] $ 3,246      
Retail [Member] | 230 White Plains Road [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1984      
Acquired 1997      
Initial Costs, Land $ 124      
Initial Costs, Building and Improvements 1,845      
Costs Capitalized Subsequent to Acquisition [1] 288      
Gross Amount at Which Carried at Close of Period, Land [2] 124      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,133      
Total [3] 2,257      
Accumulated Depreciation [4] $ 1,045      
Retail [Member] | 2 Executive Boulevard [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1986      
Acquired 1997      
Initial Costs, Land $ 89      
Initial Costs, Building and Improvements 2,439      
Costs Capitalized Subsequent to Acquisition [1] 107      
Gross Amount at Which Carried at Close of Period, Land [2] 89      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 2,546      
Total [3] 2,635      
Accumulated Depreciation [4] $ 1,324      
Multi-Family Properties [Member] | RoseGarden Monaco, L.L.C. [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2011      
Acquired 2017      
Related Encumbrances $ 169,988      
Initial Costs, Land 58,761      
Initial Costs, Building and Improvements 240,870      
Costs Capitalized Subsequent to Acquisition [1] 11      
Gross Amount at Which Carried at Close of Period, Land [2] 58,761      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 240,881      
Total [3] 299,642      
Accumulated Depreciation [4] $ 4,590      
Multi-Family Properties [Member] | Richmond Court [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1997      
Acquired 2013      
Initial Costs, Land $ 2,992      
Initial Costs, Building and Improvements 13,534      
Costs Capitalized Subsequent to Acquisition [1] 1,908      
Gross Amount at Which Carried at Close of Period, Land [2] 2,992      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 15,442      
Total [3] 18,434      
Accumulated Depreciation [4] $ 1,417      
Multi-Family Properties [Member] | Riverwatch Commons [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 1995      
Acquired 2013      
Initial Costs, Land $ 4,169      
Initial Costs, Building and Improvements 18,974      
Costs Capitalized Subsequent to Acquisition [1] 2,177      
Gross Amount at Which Carried at Close of Period, Land [2] 4,169      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 21,151      
Total [3] 25,320      
Accumulated Depreciation [4] $ 1,951      
Multi-Family Properties [Member] | Park Square [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2011      
Acquired 2013      
Related Encumbrances $ 26,526      
Initial Costs, Land 4,000      
Initial Costs, Building and Improvements 40,670      
Costs Capitalized Subsequent to Acquisition [1] 294      
Gross Amount at Which Carried at Close of Period, Land [2] 4,000      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 40,964      
Total [3] 44,964      
Accumulated Depreciation [4] $ 4,192      
Multi-Family Properties [Member] | Quarry Place At Tuckahoe [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2016      
Acquired 2016      
Related Encumbrances $ 40,367      
Initial Costs, Land 5,585      
Initial Costs, Building and Improvements 3,400      
Costs Capitalized Subsequent to Acquisition [1] 48,632      
Gross Amount at Which Carried at Close of Period, Land [2] 5,585      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 52,032      
Total [3] 57,617      
Accumulated Depreciation [4] $ 1,163      
Multi-Family Properties [Member] | Chase At Overlook Ridge [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2016      
Acquired 2016      
Related Encumbrances $ 74,988      
Initial Costs, Land 11,072      
Initial Costs, Building and Improvements 87,793      
Costs Capitalized Subsequent to Acquisition [1] 269      
Gross Amount at Which Carried at Close of Period, Land [2] 11,072      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 88,062      
Total [3] 99,134      
Accumulated Depreciation [4] $ 4,577      
Multi-Family Properties [Member] | The Chase II At Overlook Ridge [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2016      
Acquired 2016      
Related Encumbrances $ 59,697      
Initial Costs, Land 10,755      
Initial Costs, Building and Improvements 10,846      
Costs Capitalized Subsequent to Acquisition [1] 52,598      
Gross Amount at Which Carried at Close of Period, Land [2] 10,755      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 63,444      
Total [3] 74,199      
Accumulated Depreciation [4] $ 1,390      
Multi-Family Properties [Member] | Portside At Pier One [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2016      
Acquired 2016      
Related Encumbrances $ 58,566      
Initial Costs, Building and Improvements 73,713      
Costs Capitalized Subsequent to Acquisition [1] 9      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 73,722      
Total [3] 73,722      
Accumulated Depreciation [4] $ 3,908      
Multi-Family Properties [Member] | Alterra At Overlook Ridge IA [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2004      
Acquired 2013      
Related Encumbrances $ 40,061      
Initial Costs, Land 9,042      
Initial Costs, Building and Improvements 50,671      
Costs Capitalized Subsequent to Acquisition [1] 956      
Gross Amount at Which Carried at Close of Period, Land [2] 9,042      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 51,627      
Total [3] 60,669      
Accumulated Depreciation [4] $ 6,559      
Multi-Family Properties [Member] | Alterra at Overlook Ridge II [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Year Built 2008      
Acquired 2013      
Related Encumbrances $ 59,309      
Initial Costs, Land 12,055      
Initial Costs, Building and Improvements 71,409      
Costs Capitalized Subsequent to Acquisition [1] 299      
Gross Amount at Which Carried at Close of Period, Land [2] 12,056      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 71,707      
Total [3] 83,763      
Accumulated Depreciation [4] 9,058      
Projects Under Development And Developable Land [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Related Encumbrances 184,984      
Initial Costs, Land 399,372      
Initial Costs, Building and Improvements 677,593      
Gross Amount at Which Carried at Close of Period, Land [2] 399,372      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 677,593      
Total [3] 1,076,965      
Accumulated Depreciation [4] 33,278      
Furniture, Fixtures And Equipment [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Costs Capitalized Subsequent to Acquisition [1] 30,247      
Gross Amount at Which Carried at Close of Period, Building and Improvements [2] 30,247      
Total [3] 30,247      
Accumulated Depreciation [4] $ 11,031      
Buildings And Improvements [Member]        
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]        
Useful Live 40 years      
[1] These costs are net of impairments recorded, if any.
[2] The aggregate cost for federal income tax purposes at December 31, 2017 was approximately $3.9 billion.
[3] Properties identified as held for sale at December 31, 2017 are excluded.
[4] Depreciation of buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.
[5] This property is located on land leased by the Company.