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Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 USD ($) VestingInstallments $ / shares shares | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued | shares | 154,441,203 |  | 154,404,186
Common Stock, Value, Issued | $ 1,544 |  | $ 1,543
Stock based Compensation Expense | $ 14,200 | $ 10,300 |
Restricted Stock [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued | shares | 18,226 |  |
Employee and director payment per share (in dollars per share) | $ / shares | $ 0.01 |  |
Common Stock, Value, Issued | $ 2,200 |  |
Employee's weighted average cost per share (in dollars per share) | $ / shares | $ 118.98 |  |
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 | $ 36,500 |  |
Unvested MYLTIP Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Unrecognized compensation expenses | $ 26,000 |  |
Weighted-average period (years) | 2 years 9 months 18 days |  |
Boston Properties Limited Partnership | LTIP Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
LTIP units issued (in shares) | shares | 195,546 |  |
Value of LTIP units issued | $ 21,500 |  |
Per unit fair value weighted-average (in dollars per share) | $ / shares | $ 109.88 |  |
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 |  |
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 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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