v2.4.0.8

Noncontrolling Interests (Property Partnerships) (Narrative) (Details) (USD $) | 9 Months Ended |  | 0 Months Ended |  | 9 Months Ended | 0 Months Ended |  | 0 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Dec. 31, 2013 | May 31, 2013 767 Fifth Avenue (The GM Building) [Member] Consolidated Properties [Member] | Apr. 10, 2014 Salesforece Tower (formerly Transbay Tower) [Member] Consolidated Properties [Member] sqft | Sep. 30, 2013 Noncontrolling Interests [Member] | May 31, 2013 Noncontrolling Interests [Member] Consolidated Properties [Member] partners | Oct. 09, 2013 Noncontrolling Interests [Member] Time Square Tower [Member] Consolidated Properties [Member] sqft | Feb. 26, 2013 Noncontrolling Interests [Member] Salesforece Tower (formerly Transbay Tower) [Member] Consolidated Properties [Member] | Feb. 07, 2014 Noncontrolling Interests [Member] Salesforece Tower (formerly Transbay Tower) [Member] Consolidated Properties [Member]
Noncontrolling Interest [Line Items] |  |  |  |  |  |  |  |  |  |
Property partnerships | $ 716,565,000 |  | $ 726,132,000 |  |  |  |  |  |  |
Partners Joint Venture Ownership Percentage |  |  |  | 40.00% |  |  |  |  |  |
Ownership Percentage |  |  |  |  |  |  |  | 45.00% | 5.00% | 50.00%
Sales price |  |  |  |  |  |  |  | 684,000,000 |  |
Ownership Percentage by Parent |  |  |  |  | 95.00% |  |  |  | 95.00% |
Number of Joint Venture Partners |  |  |  |  |  |  | 2 |  |  |
Noncontrolling interests recorded upon consolidation | 0 | 480,861,000 |  | 480,900,000 |  | 480,861,000 |  |  |  |
maximum percentage of construction costs to allow partner to have a loan |  |  |  |  |  |  |  |  | 50.00% |
Portion of total costs partner can require the company to fund |  |  |  |  |  |  |  |  | 2.50% |
portion of partners equity that can be funded by the company |  |  |  |  |  |  |  |  | 50.00% |
Proceeds from sale of an interest in a real estate asset |  |  |  |  |  |  |  | 673,100,000 |  |
Area of Real Estate Property |  |  |  |  | 1,400,000 |  |  | 1,246,000 |  |
Portion allocation to noncontrolling interest based on carrying value of the total equity of the property prior to the sale |  |  |  |  |  |  |  | $ 243,500,000 |  |

X
- Definition maximum percentage of construction costs to allow partner to have a loan + References No definition available. + Details
Name: | bxp_Maximumpercentageofconstructioncoststoallowpartnertohavealoan
Namespace Prefix: | bxp_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Joint Venture Partners + References No definition available. + Details
Name: | bxp_NumberofJointVenturePartners
Namespace Prefix: | bxp_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Partners Joint Venture Ownership Percentage + References No definition available. + Details
Name: | bxp_PartnersJointVentureOwnershipPercentage
Namespace Prefix: | bxp_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion allocation to noncontrolling interest based on 45% of the carrying value of the total equity of the property prior to the sale + References No definition available. + Details
Name: | bxp_Portionallocationtononcontrollinginterestbasedoncarryingvalueofthetotalequityofthepropertypriortothesale
Namespace Prefix: | bxp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition portion of partners equity that can be funded by the company + References No definition available. + Details
Name: | bxp_Portionofpartnersequitythatcanbefundedbythecompany
Namespace Prefix: | bxp_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Portion of total costs partner can require the company to fund + References No definition available. + Details
Name: | bxp_Portionoftotalcostspartnercanrequirethecompanytofund
Namespace Prefix: | bxp_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Proceeds from sale of an interest in a real estate asset + References No definition available. + Details
Name: | bxp_Proceedsfromsaleofaninterestinarealestateasset
Namespace Prefix: | bxp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Area of a real estate property. + References No definition available. + Details
Name: | us-gaap_AreaOfRealEstateProperty
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation. + References No definition available. + Details
Name: | us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Carrying amount of the equity interests owned by noncontrolling partners of a limited partnership included in the entity's consolidated financial statements. + References No definition available. + Details
Name: | us-gaap_MinorityInterestInLimitedPartnerships
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_MinorityInterestLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Increase in noncontrolling interest balance because of a business combination that occurred during the period. + References No definition available. + Details
Name: | us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration