Investments in real estate, net Investment in unconsolidated entity (Details) (USD $)	6 Months Ended
Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Area of Real Estate Property	17,881,108
Greater Boston market \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Equity interest percentage (in percent)	27.50%
Equity Method Investments	$ 48,048,000
Debt Instrument, Variable Rate Base [Domain] \| Greater Boston market \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Base rate	LIBOR
Debt Instrument, Variable Rate Spread [Member] \| Greater Boston market \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Applicable margin (as a percent)	3.75%
Debt Instrument, Variable Rate Floor [Member] \| Greater Boston market \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate Floor	5.25%
Longwood [Member] \| Greater Boston market
Schedule of Equity Method Investments [Line Items]
Expected Total Joint Venture Development Cost	350,000,000
Longwood [Member] \| Greater Boston market \| Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Area of Real Estate Property	413,536
Pre-leased RSF as a Percentage of Total RSF	37.00%
Longwood [Member] \| Aggregate Commitments [Member] \| Greater Boston market
Schedule of Equity Method Investments [Line Items]
Long-term Construction Loan	213,200,000
Longwood [Member] \| Outstanding Balance [Member] \| Greater Boston market
Schedule of Equity Method Investments [Line Items]
Long-term Construction Loan	128,000,000
Longwood [Member] \| Remaining Commitments [Member] \| Greater Boston market
Schedule of Equity Method Investments [Line Items]
Long-term Construction Loan	$ 85,200,000

The minimum interest rate to be applied to the debt instrument over the course of its life.

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Expected Total Joint Venture Development Cost

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Pre-leased RSF as a Percentage of Total Project RSF

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Area of a real estate property.

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No definition available.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

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This element represents the current and noncurrent portions of a long-term real estate loan with an initial maturity beyond one year or beyond the normal operating cycle, if longer, to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project (generally one to seven years), usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property.

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