Annual report pursuant to Section 13 and 15(d)

Investments In Unconsolidated Joint Ventures (Route 93 Master LLC/Route 93 Bedford Master LLC) (Details)

v2.4.0.6
Investments In Unconsolidated Joint Ventures (Route 93 Master LLC/Route 93 Bedford Master LLC) (Details) (USD $)
In Millions, unless otherwise specified
0 Months Ended 12 Months Ended
Sep. 01, 2009
Mar. 31, 2009
Dec. 31, 2011
Jun. 01, 2006
sqft
Commingled Pension Trust Fund [Member]
       
Schedule of Equity Method Investments [Line Items]        
Ownership percentage of third party venture       70.00%
Percentage of profit/loss distribution shared by partners       60.00%
Percentage of profit/loss distribution shared by partners after internal rate of return is reached       50.00%
Route 93 Participant [Member]
       
Schedule of Equity Method Investments [Line Items]        
Percentage of profit/loss distribution shared by partners       40.00%
Percentage of profit/loss distribution shared by partners after internal rate of return is reached       50.00%
Route 93 Master LLC [Member]
       
Schedule of Equity Method Investments [Line Items]        
Percentage of interest in venture       30.00%
Number of owned office properties       7
Area of office property       666,697
Impairment of property   $ 4.0    
Impairment charges attributable to noncontrolling interest   0.6    
Spread over LIBOR 220      
Mortgage loan, maturity date July 11, 2009      
Holding and distribution pattern under operating agreement     Profits and losses were shared by the partners in proportion to their respective interests until the investment yielded an 11 percent IRR, then sharing shifted to 40/60, and when the IRR reached 15 percent, then sharing shifted to 50/50.  The Route 93 Participant is a joint venture between the Company and a Gale affiliate.  Profits and losses were shared by the partners under this venture in proportion to their respective interests (83.3/16.7) until the investment yielded an 11 percent IRR, then sharing shifted to 50/50.  
Route 93 Participant/Commingled Pension Trust Fund [Member]
       
Schedule of Equity Method Investments [Line Items]        
Joint venture investment yield percentage       11.00%
Percentage of profit/loss distribution shared by partners after internal rate of return is reached       15.00%
Route 93 Master LLC/Route 93 Bedford Master LLC [Member]
       
Schedule of Equity Method Investments [Line Items]        
Percentage of profit/loss distribution shared by partners       83.30%
Joint venture investment yield percentage       11.00%
Percentage of profit/loss distribution shared by partners after internal rate of return is reached       50.00%
Mortgage loans, carrying amount 44.2      
Gale Affiliate [Member]
       
Schedule of Equity Method Investments [Line Items]        
Percentage of profit/loss distribution shared by partners       16.70%
Percentage of profit/loss distribution shared by partners after internal rate of return is reached       50.00%