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Subsequent Events subsequent Events (Details) (USD $)
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0 Months Ended | 0 Months Ended | 0 Months Ended | |||||||||||||||
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Jul. 19, 2013
8th Avenue and 46th Street [Member]
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Jul. 01, 2013
Cambridge Center Connector [Member]
sqft
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Jul. 15, 2013
1301 New York Avenue [Member]
sqft
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Jul. 26, 2013
Minimum [Member]
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Jul. 26, 2013
Maximum [Member]
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Jul. 26, 2013
Prior to Amendment [Member]
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Jul. 26, 2013
After Amendment [Member]
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Jul. 26, 2013
After Amendment [Member]
Maximum [Member]
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Jul. 26, 2013
Interest Rate Based on LIBOR or CDOR [Member]
Minimum [Member]
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Jul. 26, 2013
Interest Rate Based on LIBOR or CDOR [Member]
Maximum [Member]
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Jul. 26, 2013
Alternative Base Interest Rate Calculation [Member]
M
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Jul. 26, 2013
Alternative Base Interest Rate Calculation [Member]
Minimum [Member]
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Jul. 26, 2013
Alternative Base Interest Rate Calculation [Member]
Maximum [Member]
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Jul. 26, 2013
Rate Based on Current Credit Rating [Member]
Interest Rate Based on LIBOR or CDOR [Member]
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Jul. 26, 2013
Rate Based on Current Credit Rating [Member]
Alternative Base Interest Rate Calculation [Member]
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Jul. 26, 2013
Rate Based on Current Credit Rating [Member]
Current Rates Based on Credit Ratings [Member]
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Aug. 07, 2013
series four preferred units [Member]
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Jun. 30, 2013
series four preferred units [Member]
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| 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 | ||||||||||||||||