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           Investments In Unconsolidated Joint Ventures (Narrative) (Details) (USD $) 
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        3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | 0 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | 6 Months Ended | 0 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | |||||||||||||||||||||||||||||
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           Mar. 31, 2009
 
          OPLP [Member] 
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           Dec. 31, 2007
 
          OPLP [Member] 
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           Jun. 30, 2011
 
          OPLP [Member] 
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           May 09, 2006
 
          OPLP [Member]
 
          sqft 
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           May 09, 2006
 
          OPLP [Member]
 
          Mack-Green [Member] 
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           Jun. 30, 2011
 
          Plaza VIII & IX Associates [Member] 
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           Jun. 30, 2011
 
          Harborside South Pier [Member] 
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           Jun. 30, 2011
 
          Red Bank Corporate Plaza [Member]
 
          sqft 
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           Mar. 31, 2011
 
          Red Bank Corporate Plaza [Member] 
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           Jun. 30, 2010
 
          Red Bank Corporate Plaza [Member] 
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           Jun. 30, 2011
 
          Red Bank Corporate Plaza [Member]
 
          sqft 
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           Jun. 30, 2010
 
          Red Bank Corporate Plaza [Member] 
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           Apr. 29, 2009
 
          Gramercy Agreement [Member] 
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           May 09, 2006
 
          Gramercy Agreement [Member] 
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           Jun. 30, 2011
 
          Gramercy Agreement [Member] 
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           Jun. 30, 2010
 
          Gramercy Agreement [Member] 
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           Mar. 31, 2010
 
          Gramercy Agreement [Member]
 
          sqft 
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           Mar. 31, 2009
 
          Gramercy Agreement [Member] 
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           Jun. 30, 2011
 
          Gramercy Agreement [Member] 
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           Jun. 30, 2010
 
          Gramercy Agreement [Member] 
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           Dec. 17, 2010
 
          Gramercy Agreement [Member]
 
          sqft 
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           Dec. 31, 2008
 
          Gramercy Agreement [Member] 
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           May 09, 2006
 
          Mack-Green [Member] 
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           Apr. 29, 2009
 
          Mack-Green [Member] 
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           Jun. 15, 2006
 
          Gale Kimball [Member]
 
          sqft 
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           Jun. 30, 2010
 
          Gale Kimball [Member] 
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           Jun. 30, 2010
 
          Gale Kimball [Member] 
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           Dec. 31, 2010
 
          Gale Kimball [Member] 
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           Jun. 30, 2011
 
          12 Vreeland [Member] 
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           Sep. 08, 2006
 
          12 Vreeland [Member]
 
          sqft 
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           Oct. 31, 2006
 
          Boston-Downtown Crossing [Member]
 
          sqft 
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           Jan. 29, 2007
 
          Boston-Downtown Crossing [Member] 
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           Dec. 31, 2008
 
          Boston-Downtown Crossing [Member] 
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           Aug. 29, 2007
 
          Gale Jefferson [Member] 
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           Jun. 30, 2011
 
          Gale Jefferson [Member] 
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           Jun. 30, 2010
 
          Gale Jefferson [Member] 
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           Jun. 30, 2011
 
          Gale Jefferson [Member] 
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           Jun. 30, 2010
 
          Gale Jefferson [Member] 
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           Aug. 22, 2007
 
          Gale Jefferson [Member]
 
          sqft 
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           May 09, 2006
 
          PFV [Member]
 
          sqft 
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           Jun. 30, 2011
 
          PFV [Member] 
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           Jun. 30, 2010
 
          PFV [Member] 
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           Jun. 30, 2010
 
          PFV [Member] 
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           Dec. 31, 2010
 
          PFV [Member] 
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           Dec. 16, 2010
 
          PFV [Member] 
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           Aug. 22, 2007
 
          M-C Jefferson [Member] 
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      |||||||
| Percentage of interest in venture | 96.00% | 100.00% | 96.00% | 50.00% | 50.00% | 50.00% | 50.00% | 100.00% | 8.33% | 50.00% | 15.00% | 10.00% | 8.33% | |||||||||||||||||||||||||||||||||||||||
| Mortgage loans, carrying amount | $ 276,300,000 | $ 65,700,000 | $ 18,500,000 | $ 20,300,000 | $ 18,500,000 | $ 90,300,000 | $ 2,300,000 | $ 21,000,000 | $ 21,000,000 | |||||||||||||||||||||||||||||||||||||||||||
| Mortgage finance on property obtained | 11,000,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of properties | 6 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Interest rate | 6.15% | 6.90% | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Mortgage loan maturity date | May 2016 | November 2016 | May 2011 | May 17, 2016 | May 2009 | July 1, 2012 | October 24, 2011 | |||||||||||||||||||||||||||||||||||||||||||||
| Date of acquisition | June 15, 2006 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Bears interest at fixed rate range, minimum | 6.09% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Bears interest at fixed rate range, maximum | 6.62% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Letter of credit | 5,900,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Area of office property | 3,500,000 | 92,878 | 92,878 | 175,000 | 139,750 | 1,200,000 | 100,010 | 527,015 | ||||||||||||||||||||||||||||||||||||||||||||
| Area of office property | 121,314 | 198,376 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Spread over LIBOR | 125 | 300 | 275 | 275 | 160 | |||||||||||||||||||||||||||||||||||||||||||||||
| LIBOR Interest Rate | 0.19% | 0.19% | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Interest rate cap | 3.15% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Venture sale of real estate | 83,500,000 | 13,900,000 | 60,000,000 | 55,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Mortgage Repayment | 1,700,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Mortgage loan refinanced amount | 18,600,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Management, leasing and other services fees | 24,000 | 24,000 | 48,000 | 48,000 | 113,000 | 234,000 | 274,000 | 467,000 | 71,800 | 142,300 | 40,000 | 94,500 | 79,000 | 131,500 | 87,000 | 213,000 | 621,000 | |||||||||||||||||||||||||||||||||||
| Acquisition cost | 125,000,000 | 1,800,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Venture property acquisition cost | 100,000,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Book value of company's long-term debt | 5,900,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Service costs | 0 | 3,000,000 | 0 | 4,000,000 | ||||||||||||||||||||||||||||||||||||||||||||||||
| Mortgage loans on real estate bearing weighted average fixed interest rate | 185,000,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Weighted average fixed interest rate | 6.26% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Loan Maturity Date | Aug. 01, 2020 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Repayments of debt | 26,800,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Share of gain on sale of real estate | 1,600,000 | 41,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of owned office properties | 25 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Number of properties sold | 8 | 1 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Venture gain (loss) on sale of real estate | 22,300,000 | 19,800,000 | 207,000 | |||||||||||||||||||||||||||||||||||||||||||||||||
| Impairment charge on property | 32,300,000 | 69,500,000 | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Sharing percent of amount realized | 50.00% | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Distribution received from venture | 2,400,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Distribution received | $ 5,400,000 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| Holding and distribution pattern under operating agreement | 
 The Mack-Green operating agreement generally provided for profits and losses to be allocated as follows: 
 
 (iii) 50 percent of all other profits and losses allocable to the Company and 50 percent allocable to SL Green.  | 
        
 Under the operating agreement of 12 Vreeland Associates, L.L.C., M-C Vreeland has a 50 percent interest, with S/K Florham Park Associates, L.L.C. (the managing member) and its affiliate holding the other 50 percent. 
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 Distributions will generally be in proportion to its members' respective ownership interests and, depending upon the development unit, promotes will be available to specified partners after the achievement of certain internal rates of return ranging from 10 to 15 percent.  | 
        
 The operating agreement of M-C Jefferson provides, among other things, for the Participation Rights (see Note 15: Noncontrolling Interests in Subsidiaries – Participation Rights).  The operating agreements of Gale Jefferson, L.L.C. ("Gale Jefferson"), which is owned 33.33 percent by M-C Jefferson and 66.67 percent by the Hampshire Generational Fund, L.L.C. ("Hampshire") provides, among other things, for the distribution of net cash flow, first, in accordance with its member's respective interests until each member is provided, as a result of such distributions, with an annual 12 percent compound return on the Member's Capital Contributions, as defined in the operating agreement and secondly, 50 percent to each of the Company and Hampshire. 
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