Acres Of Land.

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Development Revenue.

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Disposition Price.

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Gross Proceeds From Transaction.

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Gross Proceeds From Transaction Received.

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Ground Lease Payments Per Year

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Office Component Placed In Service

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Percentage Of Development Leased.

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Placed In Service Percentage.

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Square Footage Of Signed Lease.

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Amount of cash paid to acquire the entity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

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Interest rate stated in the contractual debt agreement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The number of real estate properties owned as of the balance sheet date.

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Real Estate Activity During The Nine Months Ended September 30, 2011 (Narrative) (Details) (USD $)	0 Months Ended				9 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended							9 Months Ended	0 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	May 23, 2011 Anticipated Through Q3 2014 [Member] 75 Ames Street [Member]	Feb. 01, 2011 Bay Colony Corporate Center [Member]	Sep. 30, 2011 Bay Colony Corporate Center [Member]	Jan. 14, 2011 Atlantic Wharf Development [Member]	Sep. 30, 2011 Atlantic Wharf Development [Member]	Mar. 01, 2011 Pennsylvania Avenue Development [Member]	May 01, 2011 510 Madison Avenue [Member]	May 11, 2011 2221 I Street [Member]	Jul. 05, 2011 One Two Three One Zero Sunrise Valley Drive [Member]	May 24, 2011 250 West 55th Street [Member]	Jun. 06, 2011 Carnegie Center [Member]	May 23, 2011 75 Ames Street [Member]	Sep. 30, 2011 75 Ames Street [Member]	Jul. 14, 2011 Cambridge Center [Member]
Real Estate Properties [Line Items]
Acquisition date				February 1, 2011
Acquisition aggregate purchase price				$ 185,000,000	$ 185,000,000
Cash portion of purchase price				41,100,000
Portion of acquisition included in debt				143,900,000	143,900,000
Interest at a fixed rate	2.875%	3.70%		6.53%
Maturity date	Feb. 15, 2037	Nov. 15, 2018		Jun. 11, 2012
Square footage of real estate property				966,000		790,000	10,000	457,000	347,000	50,000	268,000	989,000	2,000,000	250,000		190,000
Square footage of signed lease												184,000
Number of real estate properties				4									16
Number of units in real estate property							86			335
Acres of land				58									560
Office component placed in-service (percentage)						57.00%		13.00%
Placed in-service (percentage)							100.00%		16.00%
Gross proceeds from transaction														56,800,000
Gross proceeds from transaction received															48,000,000
Development revenue			8,900,000											11,400,000
Disposition price													468,000,000
Approximate proceeds per year from ground lease														$ 459,000
Term of lease (years)														99		15
Percentage of development leased																100.00%