v2.4.0.8

Subsequent Events subsequent Events (Details) (USD $)	9 Months Ended															0 Months Ended											0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Nov. 01, 2014 535 Mission Street [Member] Subsequent Event [Member] sqft	Oct. 22, 2014 415 Main Street (formerly Seven Cambridge Center) [Member] Subsequent Event [Member] sqft leaseyear	Nov. 06, 2014 425 Main Street [Member] Subsequent Event [Member]	Jun. 11, 2014 Patriots park [Member] Buildings sqft	Oct. 02, 2014 Patriots park [Member] Subsequent Event [Member] sqft Buildings	Oct. 24, 2014 130 Third Avenue [Member] Subsequent Event [Member] sqft	Sep. 30, 2014 Noncontrolling Interests [Member]	Sep. 30, 2014 Series Four Preferred Units [Member] Noncontrolling Interests [Member]	Jul. 03, 2014 Series Four Preferred Units [Member] Noncontrolling Interests [Member]	May 19, 2014 Series Four Preferred Units [Member] Noncontrolling Interests [Member]	Nov. 05, 2014 Series Four Preferred Units [Member] Noncontrolling Interests [Member] Subsequent Event [Member]	Oct. 16, 2014 Series Four Preferred Units [Member] Noncontrolling Interests [Member] Subsequent Event [Member]	Oct. 24, 2014 Annapolis Junction Building Six [Member] Subsequent Event [Member] sqft	Oct. 24, 2014 Construction Loans [Member] Annapolis Junction Building Six [Member] Subsequent Event [Member]	Oct. 23, 2014 Construction Loans [Member] Annapolis Junction Building Six [Member] Subsequent Event [Member]	Oct. 24, 2014 Construction Loans [Member] Annapolis Junction Building Six [Member] Subsequent Event [Member]	Sep. 16, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member]	Oct. 30, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] Subsequent Event [Member]	Sep. 16, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] sqft	Oct. 30, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] Subsequent Event [Member] sqft	Sep. 16, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] Atlantic Wharf Office [Member] sqft	Oct. 30, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] Atlantic Wharf Office [Member] Subsequent Event [Member] sqft	Sep. 16, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 100 Federal Street [Member] sqft	Oct. 30, 2014 Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 100 Federal Street [Member] Subsequent Event [Member] sqft	Sep. 16, 2014 Office Tower [Member] Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] floor	Oct. 30, 2014 Office Tower [Member] Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] Subsequent Event [Member] floor	Sep. 16, 2014 Low Rise [Member] Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] floor	Oct. 30, 2014 Low Rise [Member] Consolidated Properties [Member] 601 Lexington Avenue, Atlantic Wharf Office Building and One Hundred Federal Street [Member] 601 Lexington Avenue [Member] Subsequent Event [Member] floor	Nov. 03, 2014 Unsecured Debt [Member] Subsequent Event [Member] 5.625% Unsecured Senior Notes [Member]	Nov. 03, 2014 Unsecured Debt [Member] Subsequent Event [Member] 5% Unsecured Senior Notes [Member]
Subsequent Event [Line Items]
Sales price						$ 321,000,000	$ 321,000,000	$ 14,300,000
Ownership Percentage															50.00%
Construction Loan																		13,900,000
Debt Instrument, Basis Spread on Variable Rate																2.25%	1.65%
Construction Loan Facility Borrowing Capacity																		16,400,000
Debt Instrument, Description of Variable Rate Basis																LIBOR	LIBOR
Area of Real Estate Property			307,000	231,000		706,000	706,000	129,000							119,000						1,669,000	1,669,000	791,000	791,000	1,323,000	1,323,000
Series Four Preferred Units Released from Escrow												319,687		27,773
Redemption of Series Four Preferred Units											16,000,000		1,400,000
Series Four Preferred Units (in shares)									40,440	40,440	40,440		12,667
Purchase Option Price for Real Estate Property				106,000,000
Purchase option date (lease year)				11
Repayments of Secured Debt	82,030,000	96,750,000
Coupon/Stated Rate																															5.625%	5.00%
Number of real estate properties						3	3
Ownership Percentage																			45.00%	45.00%
Gross Sales Price Before Deducting Indebtedness																			1,827,000,000	1,827,000,000
Number of floors real estate																											59	59	6	6
Secured Debt Carrying Value																			712,900,000	712,900,000
Debt Instrument, Repurchased Face Amount																															300,000,000	250,000,000
Basis Points Added to US Treasury Security Used in Redemption Price																															0.35%	0.25%
Non-refundable option payment					$ 1,000,000

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Basis Points Added to US Treasury Security Used in Redemption Price

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Construction Loan Facility Borrowing Capacity

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Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation before deducting indebtedness.

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Amount classified as secured debt attributable to disposal group held for sale or disposed of.

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- Definition

Non-refundable option payment

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Number of floors real estate

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- Definition

Purchase option date (lease year)

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Purchase Option Price for Real Estate Property

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- Definition

Redemption of Series Four Preferred Units

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Series Four Preferred Units

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Series Four Preferred Units Released from Escrow

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Area of a real estate property.

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This element represents the carrying value of a short-term real estate loan 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, 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. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



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-Number 210

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-Paragraph 19, 20

-Article 5

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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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Contractual interest rate for funds borrowed, under the debt agreement.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



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Face (par) amount of the original debt instrument that was repurchased.

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Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

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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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585



Reference 2: http://www.xbrl.org/2003/role/presentationRef

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