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Summary Of Significant Accounting Policies (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) yr | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Entity Information [Line Items] |  |  |
Probable Sale Term of Property After Classified As Held For Sale (Years) | yr | 1 |  |
Maximum Period After Construction The Company Considers A Construction Project As Substantially Completed (In Years) | yr | 1 |  |
Interest costs capitalized | $ 61,070,000 | $ 39,237,000 | $ 34,213,000
Salaries And Related Costs Capitalized | 13,200,000 | 11,100,000 | 10,400,000
Cash FDIC Insured Limit | 250,000 |  |
Separate Unrestricted Cash For Deferred Compensation Plan. | 29,200,000 | 23,800,000 |
Gains (losses) from investments in securities | 3,678,000 | 2,273,000 | (653,000)
Internal Leasing Salaries And Related Costs Capitalized | 5,000,000 | 7,200,000 | 5,500,000
Straight-line rent adjustments | (54,800,000) | (31,700,000) | (80,000,000)
Above and below market rent adjustments, net | $ 23,500,000 | 30,200,000 | 35,900,000
Ground Lease Expiration Date, Maximum | 2114 |  |
REIT Annual Taxable Income Distribution Requirement Percentage, Minimum | 90.00% |  |
Company Annual Taxable Income Distribution Percentage | 100.00% |  |
Net Difference Between Tax Basis And Company's Assets And Liabilities. | $ 1,800,000,000 | 1,700,000,000 |
Debt Issuance Costs, Net | 34,680,000 |  |
Cumulative effect of a change in accounting principle | 2,035,000 |  |
Boston Properties Limited Partnership |  |  |
Entity Information [Line Items] |  |  |
Interest costs capitalized | 61,070,000 | 39,237,000 | 34,213,000
Gains (losses) from investments in securities | 3,678,000 | 2,273,000 | $ (653,000)
Net Difference Between Tax Basis And Company's Assets And Liabilities. | 2,900,000,000 | $ 2,700,000,000 |
Debt Issuance Costs, Net | 34,700,000 |  |
Cumulative effect of a change in accounting principle | 272,000 |  |
Dividends In Excess Of Earnings [Member] |  |  |
Entity Information [Line Items] |  |  |
Cumulative effect of a change in accounting principle | 272,000 |  |
Noncontrolling Interests [Member] |  |  |
Entity Information [Line Items] |  |  |
Cumulative effect of a change in accounting principle | 1,763,000 |  |
Noncontrolling Interests [Member] | Boston Properties Limited Partnership |  |  |
Entity Information [Line Items] |  |  |
Cumulative effect of a change in accounting principle | $ 1,763,000 |  |

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