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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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-Publisher FASB
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-Topic 718
-SubTopic 10
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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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Number of shares (or other type of equity) forfeited during the period.

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Stock Option and Incentive Plan (Narrative) (Details) $ / shares in Units, $ in Millions	Feb. 09, 2019 USD ($) shares	Feb. 05, 2019 USD ($) shares	Feb. 04, 2018 USD ($) shares	Feb. 03, 2017 USD ($) shares	May 15, 2012 shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Exercisable						540,441	540,441
Exercisable, Weighted Average Exercise Price \| $ / shares						$ 96.35	$ 96.35
2012 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Additional Shares Authorized					13,000,000
Other Than Stock Options Awards Conversion Ratio					2.32
Stock Option Awards Conversion Ratio					1.0
Stock Option and Incentive Plan Term Period					10 years
MYLTIP 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		4 years
TSR measurement (in years)		three-year
Minimum earned awards		0
Maximum Earned Awards		220,734
Earned wards - Target		110,367
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights		Earned awards (if any) will vest 50% on February 4, 2022 and 50% on February 4, 2023, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by Boston Properties, Inc. without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 4, 2022, earned awards will be calculated based on TSR performance up to the date of the change of control. The 2019 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units.
Value of MYLTIP Awards \| $		$ 13.5
MYLTIP Value Amortized Into Earnings, Years		four year
MYLTIP 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $				$ 3.5
Final awards percentage of target				27.70%
MYLTIP Units forfeited				447,386
MYLTIP 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $	$ 13.6
Stock Issued During Period, Shares, Share-based Compensation, Forfeited	364,980
Final awards percentage of target	69.50%
MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards \| $			$ 3.6
Final awards percentage of target			22.00%
MYLTIP Units forfeited			337,847