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Segment Information Narrative (Details) - Los Angeles [Member] ft² in Millions | Sep. 30, 2019 ft² Buildings
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Segment Reporting Information [Line Items] |
Net Rentable Area (in sf) | ft² | 2.3
Number of real estate properties | Buildings | 27

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- Definition Net rentable area for properties owned. + References No definition available. + Details
Name: | us-gaap_NetRentableArea
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of real estate properties owned as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfRealEstateProperties
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_StatementGeographicalAxis=bxp_LosAngelesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |