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Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2017 USD ($) VestingInstallments d $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares | May 17, 2016 shares | Jan. 01, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares issued | 154,404,186 | 153,869,075 |  | 1,507 |
Stock-based compensation associated with restricted stock, non-qualified options, LTIP Units, 2012 OPP Units and 2013-2017 MYLTIP Units | $ | $ 33,200 | $ 30,600 | $ 26,900 |  |
Value of shares of common stock | $ | 1,543 | $ 1,538 |  |  |
Exercisable, Weighted Average Exercise Price | $ / shares |  | $ 96.32 | $ 96.10 |  |
Total intrinsic value of the outstanding and exercisable stock options | $ | $ 18,200 |  |  |  |
Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares issued | 37,414 | 22,067 | 34,150 |  |
Employee and director payment per share (in dollars per share) | $ / shares | $ 0.01 |  |  |  |
Value of shares of common stock | $ | $ 4,900 | $ 2,500 | $ 4,800 |  |
Employee's weighted average cost per share (in dollars per share) | $ / shares | $ 130.32 | $ 113.51 | $ 140.88 |  |
LTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of LTIP units issued | $ | $ 13,600 | $ 15,400 | $ 13,500 |  |
Per unit fair value weighted-average (in dollars per share) | $ / shares | $ 119.41 | $ 103.83 | $ 128.94 |  |
Expected life assumed to calculate per unit fair value per LTIP unit (years) | 5 years 8 months 12 days | 5 years 8 months 12 days | 5 years 8 months 12 days |  |
Risk-free rate | 2.14% | 1.61% | 1.47% |  |
Expected price volatility | 28.00% | 33.00% | 26.00% |  |
Unvested Restricted stock, LTIP and 2013 - 2014 MYLTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Unrecognized compensation expenses | $ | $ 19,200 |  |  |  |
LTIPs And Restricted Stock [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting annual installments | VestingInstallments | 4 |  |  |  |
Unvested 2015 - 2017 MYLTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Unrecognized compensation expenses | $ | $ 21,000 |  |  |  |
Weighted-average period (years) | 2 years 3 months 18 days |  |  |  |
LTIPs, OPP and MYLTIP Awards [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 |  |  |  |
MYLTIP 2015 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
MYLTIP units issued |  |  | 375,000 |  |
MYLTIP 2016 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
MYLTIP units issued |  | 475,004 |  |  |
Non-Qualified Employee Stock Purchase Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Maximum Common Stock available for issuance | 250,000 |  |  |  |
Employee Common Stock options, percent of average closing price | 85.00% |  |  |  |
Number Of Days Used In Calculation, Average Closing Prices Of Common Stock | d | 10 |  |  |  |
Shares issued | 6,317 | 5,695 | 6,199 |  |
Shares issued, weighted-average purchase price per share | $ / shares | $ 105.97 | $ 109.27 | $ 108.73 |  |
Boston Properties Limited Partnership | LTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
LTIP units issued (in shares) | 113,918 | 147,872 | 190,563 |  |
Boston Properties Limited Partnership | MYLTIP 2017 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
MYLTIP units issued | 400,000 |  |  |  |
Boston Properties Limited Partnership | Non-executive Chairman of the Board of Directors [Member] | LTIP Units [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
LTIP units issued (in shares) |  |  |  |  | 85,962

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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=6415400&loc=d3e5070-113901 + Details
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