v2.4.0.8

Subsequent Events subsequent Events (Details) (USD $) | 0 Months Ended |  |  | 0 Months Ended |  | 0 Months Ended |  |
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Jul. 19, 2013 8th Avenue and 46th Street [Member] | Jul. 01, 2013 Cambridge Center Connector [Member] sqft | Jul. 15, 2013 1301 New York Avenue [Member] sqft | Jul. 26, 2013 Minimum [Member] | Jul. 26, 2013 Maximum [Member] | Jul. 26, 2013 Prior to Amendment [Member] | Jul. 26, 2013 After Amendment [Member] | Jul. 26, 2013 After Amendment [Member] Maximum [Member] | Jul. 26, 2013 Interest Rate Based on LIBOR or CDOR [Member] Minimum [Member] | Jul. 26, 2013 Interest Rate Based on LIBOR or CDOR [Member] Maximum [Member] | Jul. 26, 2013 Alternative Base Interest Rate Calculation [Member] M | Jul. 26, 2013 Alternative Base Interest Rate Calculation [Member] Minimum [Member] | Jul. 26, 2013 Alternative Base Interest Rate Calculation [Member] Maximum [Member] | Jul. 26, 2013 Rate Based on Current Credit Rating [Member] Interest Rate Based on LIBOR or CDOR [Member] | Jul. 26, 2013 Rate Based on Current Credit Rating [Member] Alternative Base Interest Rate Calculation [Member] | Jul. 26, 2013 Rate Based on Current Credit Rating [Member] Current Rates Based on Credit Ratings [Member] | Aug. 07, 2013 series four preferred units [Member] | Jun. 30, 2013 series four preferred units [Member]
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contractual Sales Price |  |  | $ 135,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area |  | 43,000 | 201,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Contractual Sales Price |  |  | 121,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Imputed Sales Price | 45,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Net Sales Proceeds | 21,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  |  |  |  |  | 750,000,000 | 1,000,000,000 |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Expiration Date |  |  |  |  |  | Jun. 24, 2014 | Jul. 26, 2018 |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity |  |  |  |  |  |  |  | $ 1,500,000,000 |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  |  |  |  |  |  |  |  | 0.925% | 1.70% |  | 0.00% | 0.70% | 1.00% | 0.00% |  |  |
Amount added to Federal Funds Rate to Calculate Interest Rate |  |  |  |  |  |  |  |  |  |  | 0.50% |  |  |  |  |  |  |
LIBOR Period Used to Calculate Interest Rate (in months) |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Amount added to LIBOR to Calculate Interest Rate |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  |  |  | 0.125% | 0.35% |  |  |  |  |  |  |  |  |  |  | 0.15% |  |
Series Four Preferred Units Redeemed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 861,400 |
Preferred Units Liquidation Preference |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 50.00 | $ 50.00

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