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Summary Of Significant Accounting Policies (Narrative) (Details) $ in Thousands |  | 6 Months Ended
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Jan. 01, 2020 USD ($) | Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |
Number of VIEs |  | 6 |
Number of VIEs - Total |  | 7 |
Cumulative effect of a change in accounting principle |  | $ (1,679) | $ (4,379)
Dividends In Excess Of Earnings [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cumulative effect of a change in accounting principle | $ 1,500 | (1,505) | (3,864)
Dividends In Excess Of Earnings [Member] | Boston Properties Limited Partnership |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cumulative effect of a change in accounting principle | 1,500 |  |
Noncontrolling Interests [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cumulative effect of a change in accounting principle | 200 | (174) | (445)
Noncontrolling Interests [Member] | Boston Properties Limited Partnership |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cumulative effect of a change in accounting principle | $ 200 |  |
Noncontrolling interest - property partnerships [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cumulative effect of a change in accounting principle |  | $ 0 | $ (70)

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- Definition Amount of the cumulative effect on retained earnings net of related income tax effect. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794 + Details
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