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Stock Option and Incentive Plan Restricted Stock (Narrative) (Details) $ / shares in Units, $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 USD ($) $ / shares shares | Mar. 31, 2018 USD ($) | Dec. 31, 2018 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued | shares | 154,594,386 |  | 154,537,378
Common Stock, Value, Issued | $ 1,545 |  | $ 1,545
Stock based compensation expense | $ 14,800 | $ 14,200 |
Restricted Stock [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares issued | shares | 23,083 |  |
Employee and director payment per share (in dollars per share) | $ / shares | $ 0.01 |  |
Common Stock, Value, Issued | $ 3,000 |  |
Employee's weighted average cost per share (in dollars per share) | $ / shares | $ 131.23 |  |
LTIP Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Value of LTIP units issued | $ 20,900 |  |
Per unit fair value weighted-average (in dollars per share) | $ / shares | $ 121.41 |  |
Expected life assumed to calculate per unit fair value per LTIP unit (years) | 5 years 8 months 12 days |  |
Risk-free rate | 2.68% |  |
Expected price volatility | 27.00% |  |
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 | 4 |  |
Unrecognized compensation expenses | $ 38,400 |  |
Unvested MYLTIP Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Unrecognized compensation expenses | $ 22,600 |  |
Weighted-average period (years) | 2 years 10 months 24 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 | 172,166 |  |
Boston Properties Limited Partnership | 2019 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
MYLTIP units issued (in shares) | shares | 220,734 |  |
Boston Properties Limited Partnership | LTIPs and 2019 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&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://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&loc=d3e5070-113901 + Details
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