Debt Instrument, Extended Maturity Period

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- Definition

Debt Instrument, Number of One-Year Maturity Date Extension Option

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No definition available.

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- Definition

Debt key terms [Abstract]

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No definition available.

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- Definition

Earn-out provisions for incremental borrowing

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- Definition

Gain (Loss) on Sale of Rental Properties, Net of Applicable Income Taxes

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No definition available.

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- Definition

Long-term Debt, Percentage Bearing Fixed Interest, Remaining Commitments

+ References

No definition available.

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- Definition

Long-term Debt, Percentage Bearing Variable Interest, Remaining Commitments

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No definition available.

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- Definition

Percentage to Total Rentable Square Feet of Operating Property

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No definition available.

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- Definition

Area of a real estate property.

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No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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- Definition

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

+ References

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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- Definition

This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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-Name Accounting Standards Codification
-Topic 225
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-Section S99
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Investment in unconsolidated real estate joint ventures Investment in unconsolidated real estate joint ventures (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) ft² Extension_Option	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) ft² Extension_Option	Sep. 30, 2016 USD ($)	Jun. 30, 2017 ft²
Schedule of Equity Method Investments [Line Items]
Gain (loss) on sale of real estate - rental properties	$ 0	$ 0	$ 270,000	$ 0
Distributions of earnings from unconsolidated real estate joint ventures			$ 249,000	$ 286,000
Debt key terms [Abstract]
Weighted-Average Interest Rate at End of Period (as a percent)	3.76%		3.76%
Long-term Debt	$ 4,817,040,000		$ 4,817,040,000
Outstanding Balance	$ 4,828,766,000		4,828,766,000
Greater Boston market \| 360 Longwood Avenue
Schedule of Equity Method Investments [Line Items]
Area of Real Estate Property \| ft²					413,799
Distributions of earnings from unconsolidated real estate joint ventures			$ 38,800,000
Greater Boston market \| 360 Longwood Avenue \| Secured debt maturing on 9/1/22
Debt key terms [Abstract]
Debt Instrument, Number of One-Year Maturity Date Extension Option \| Extension_Option	2		2
Debt Instrument, Extended Maturity Period			1 year
Earn-out provisions for incremental borrowing	$ 48,000,000.000		$ 48,000,000.000
Greater Boston market \| 360 Longwood Avenue \| $95 million secured debt maturing on 9/1/22
Debt key terms [Abstract]
Maturity Date			Sep. 01, 2022
Stated interest rate (as a percent)	3.32%		3.32%
Weighted-Average Interest Rate at End of Period (as a percent)	3.62%		3.62%
Long-term Debt	$ 94,086,000		$ 94,086,000
Outstanding Balance	95,000,000		95,000,000
Remaining Commitments of Long-term Debt at Fixed Interest	0		0
Long-term debt at fixed interest rate	$ 95,000,000		$ 95,000,000
Greater Boston market \| 360 Longwood Avenue \| $17 million secured debt maturing on 9/1/22
Debt key terms [Abstract]
Maturity Date			Sep. 01, 2022
Weighted-Average Interest Rate at End of Period (as a percent)	0.00%		0.00%
Long-term Debt	$ 0		$ 0
Outstanding Balance	0		0
Remaining Commitments of Long-term Debt at Variable Interest	17,000,000		17,000,000
Long-term debt at variable interest rate	$ 17,000,000		$ 17,000,000
Greater Boston market \| London Interbank Offered Rate (LIBOR) \| 360 Longwood Avenue \| $17 million secured debt maturing on 9/1/22
Debt key terms [Abstract]
Applicable margin (as a percent)			1.85%
Longwood Condomium \| Greater Boston market \| 360 Longwood Avenue
Schedule of Equity Method Investments [Line Items]
Area of Real Estate Property \| ft²	203,090		203,090
Percentage to Total Rentable Square Feet of Operating Property	49.00%		49.00%
Gain (loss) on sale of real estate - rental properties	$ 14,100,000
Equity Method Investee \| Greater Boston market \| 360 Longwood Avenue
Schedule of Equity Method Investments [Line Items]
Equity interest percentage (in percent)	27.50%		27.50%