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Stock Option and Incentive Plan Restricted Stock (Narrative) (Details) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 USD ($) $ / shares shares | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) VestingInstallments $ / shares shares | Sep. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares issued | shares | 154,519,139 |  | 154,519,139 |  | 154,404,186
Common Stock, Value, Issued | $ 1,544 |  | $ 1,544 |  | $ 1,543
Stock based compensation expense | $ 7,900 | $ 7,500 | $ 30,100 | $ 25,600 |
Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares issued | shares | 20,320 |  | 20,320 |  |
Employee and director payment per share (in dollars per share) | $ / shares |  |  | $ 0.01 |  |
Common Stock, Value, Issued | $ 2,400 |  | $ 2,400 |  |
Employee's weighted average cost per share (in dollars per share) | $ / shares | $ 119.27 |  | $ 119.27 |  |
LTIPs (including vested 2012 OPP Awards and vested MYLTIPS) And Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting annual installments | VestingInstallments |  |  | 4 |  |
Unrecognized compensation expenses | $ 27,300 |  | $ 27,300 |  |
Unvested MYLTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Unrecognized compensation expenses | $ 18,800 |  | $ 18,800 |  |
Weighted-average period (years) | 2 years 6 months |  |  |  |
Boston Properties Limited Partnership | LTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
LTIP units issued (in shares) | shares | 205,838 |  | 205,838 |  |
Value of LTIP units issued |  |  | $ 22,700 |  |
Per unit fair value weighted-average (in dollars per share) | $ / shares | $ 110.29 |  | $ 110.29 |  |
Expected life assumed to calculate per unit fair value per LTIP unit (years) |  |  | 5 years 8 months 12 days |  |
Risk-free rate |  |  | 2.63% |  |
Expected price volatility |  |  | 27.00% |  |
Boston Properties Limited Partnership | 2018 MYLTIP [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
MYLTIP units issued (in shares) | shares | 342,659 |  | 342,659 |  |
Boston Properties Limited Partnership | LTIPs and 2018 MYLTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Employee and director payment per share (in dollars per share) | $ / shares |  |  | $ 0.25 |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + 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(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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