Contractual Sales Price

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- Definition

Ground Lease Term (in years)

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Number of floors real estate

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Number of apartment units that could potentially be built under an option agreement

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Portion of Building Leased (percentage)

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- Definition

Sale Price Of Sold Property

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- Definition

Term of Lease Signed (in years)

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of assets acquired at the acquisition date.

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- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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This element represents the amount of gain (loss) on sale of properties during the reporting period gross of the applicable income taxes realized.

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The charge against earnings in the period to reduce the carrying amount of real property to fair value.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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- Definition

Net rentable area for properties owned.

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No definition available.

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- Definition

Amount after tax of income (loss) attributable to nonredeemable noncontrolling partner of a limited partnership.

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The net result for the period of deducting operating expenses from operating revenues.

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No definition available.

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- Definition

The cash outflow from the acquisition of a piece of land and anything permanently fixed to it, including buildings, structures on it and so forth, and payments to develop real estate assets by adding improvements on or to a parcel of land. Such improvements may include drainage, utilities, subdividing, access, buildings, and any combination of these elements. Including real estate intended to generate income for the owner; excluding real estate acquired for use by the owner.

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Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets.

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- Definition

Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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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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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Real Estate (Narrative) (Details) $ in Thousands					1 Months Ended	3 Months Ended								8 Months Ended	12 Months Ended
Real Estate (Narrative) (Details) $ in Thousands	Dec. 06, 2016 USD ($) ft² yr	Aug. 19, 2016 USD ($) ft² floor	Aug. 16, 2016 USD ($)	Feb. 01, 2016 USD ($) ft²	Jan. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 29, 2016 ft²	Nov. 14, 2016 USD ($)	Nov. 07, 2016 ft² yr	Oct. 24, 2016 apartments	Sep. 16, 2016 ft²	Jun. 24, 2016 ft²	May 27, 2016 ft²	Apr. 22, 2016 USD ($) ft²	Feb. 03, 2016 ft²
Real Estate Properties [Line Items]
Payments to Acquire and Develop Real Estate															$ 78,000	$ 0	$ 4,670
Total revenue						$ 636,061	$ 625,228	$ 623,546	$ 665,985	$ 624,240	$ 629,884	$ 618,221	$ 618,476		2,550,820	2,490,821	2,396,998
Earnings															825,784	849,365	801,822
Proceeds from sales of real estate															122,750	602,600	419,864
Prepaid ground rent						129,666				185,118				$ 129,666	129,666	185,118
Accelerated depreciation related to redevelopment															694,403	639,542	628,573
Accelerated depreciation associated with redevelompent allocated to the outside partners'															(2,068)	149,855	30,561
Impairment loss															1,783	0	0
Gains on sales of real estate															80,606	375,895	168,039
Impairment loss															1,783	0	0
3625-3635 Peterson Way
Real Estate Properties [Line Items]
Net assets acquired																									$ 78,000
Total revenue														3,900
Earnings														200
Net Rentable Area \| ft²																									218,000
Portion of Building Leased (percentage)																									100.00%
415 Main Street
Real Estate Properties [Line Items]
Earnings					$ 1,200											8,300	8,200
Proceeds from sales of real estate				$ 104,900
Net Rentable Area \| ft²				231,000
Sale Price Of Sold Property				$ 105,400
Gains on sales of real estate				60,800
Broad Run Business Park
Real Estate Properties [Line Items]
Proceeds from sales of real estate			$ 17,900
Sale Price Of Sold Property			18,000
Gains on sales of real estate			$ 13,000
601 Lexington Avenue \| Consolidated Properties [Member]
Real Estate Properties [Line Items]
Ownership Percentage by Parent		55.00%
Number of floors in building \| floor		6
Accelerated depreciation related to redevelopment		$ 50,800
Accelerated depreciation associated with redevelompent allocated to the outside partners'		$ 21,400
888 Boylston Street
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																						425,000
145 Broadway
Real Estate Properties [Line Items]
Term of Lease Signed (in years) \| yr																				15
191 Spring Street
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																		160,000
601 Massachusetts Avenue
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																								479,000
804 Carnegie Center [Member]
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																								130,000
10 CityPoint
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																							241,000
MacArthur Station
Real Estate Properties [Line Items]
Number of apartment units \| apartments																					400
2100 Pennsylvania Avenue [Member]
Real Estate Properties [Line Items]
Ground Lease Term (in years) \| yr	75
Prepaid ground rent	$ 15,000
Future development [Member] \| 3625-3635 Peterson Way
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																									632,000
Future development [Member] \| 145 Broadway
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																				476,500
Future development [Member] \| 2100 Pennsylvania Avenue [Member]
Real Estate Properties [Line Items]
Net Rentable Area \| ft²	482,000
Land [Member] \| Washingtonian North
Real Estate Properties [Line Items]
Contractual Sales Price																			$ 7,800
Impairment loss															1,800
Office Building [Member] \| 601 Lexington Avenue \| Consolidated Properties [Member]
Real Estate Properties [Line Items]
Net Rentable Area \| ft²		195,000
Office Building [Member] \| 145 Broadway
Real Estate Properties [Line Items]
Net Rentable Area \| ft²																				80,000
Retail Site [Member] \| 601 Lexington Avenue \| Consolidated Properties [Member]
Real Estate Properties [Line Items]
Net Rentable Area \| ft²		25,000
Terminated lease at 250 West 55th Street in NYC [Member]
Real Estate Properties [Line Items]
Total revenue															45,000
Net Rentable Area \| ft²																										85,000
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Payments to Acquire and Develop Real Estate															78,000	0	4,670
Total revenue						636,061	$ 625,228	$ 623,546	$ 665,985	624,240	$ 629,884	$ 618,221	$ 618,476		2,550,820	2,490,821	2,396,998
Earnings															837,411	857,358	810,331
Proceeds from sales of real estate															122,750	602,600	419,864
Prepaid ground rent						$ 129,666				$ 185,118				$ 129,666	129,666	185,118
Accelerated depreciation related to redevelopment															682,776	631,549	620,064
Accelerated depreciation associated with redevelompent allocated to the outside partners'															(2,068)	149,855	30,561
Impairment loss															1,783	0	0
Gains on sales of real estate															82,775	377,093	174,686
Impairment loss															$ 1,783	$ 0	$ 0
Boston Properties Limited Partnership \| 415 Main Street
Real Estate Properties [Line Items]
Gains on sales of real estate				$ 63,000
Boston Properties Limited Partnership \| 601 Lexington Avenue \| Consolidated Properties [Member]
Real Estate Properties [Line Items]
Accelerated depreciation related to redevelopment		$ 47,600