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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]    
Carrying value of the Company's investments in unconsolidated joint ventures $ 196,188us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 193,394us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
Square 407 Limited Partnership [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties Market Square North  
Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_SquareFourZeroSevenLimitedPartnershipMember		  
Carrying value of the Company's investments in unconsolidated joint ventures (7,345)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_SquareFourZeroSevenLimitedPartnershipMember		 [1]  
The Metropolitan Square Associates LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties Metropolitan Square  
Ownership Percentage 51.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_MetropolitanSquareAssociatesLlcMember		  
Carrying value of the Company's investments in unconsolidated joint ventures 8,850us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_MetropolitanSquareAssociatesLlcMember		 [1]  
BP/CRF 901 New York Avenue LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties 901 New York Avenue  
Ownership Percentage 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_BpCrfNineZeroOneNewYorkAvenueLlcMember		 [2]  
Carrying value of the Company's investments in unconsolidated joint ventures (12,907)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_BpCrfNineZeroOneNewYorkAvenueLlcMember		 [1]  
WP Project Developer LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties Wisconsin Place Land and Infrastructure  
Ownership Percentage 33.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_WpProjectDeveloperLlcMember		 [3]  
Carrying value of the Company's investments in unconsolidated joint ventures 45,283us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_WpProjectDeveloperLlcMember		 [1]  
Annapolis Junction NFM, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties Annapolis Junction  
Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		 [4]  
Carrying value of the Company's investments in unconsolidated joint ventures 25,935us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		 [1]  
Number of real estate properties 2us-gaap_NumberOfRealEstateProperties
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		  
Number of buildings under construction 2bxp_NumberOfBuildingsUnderConstruction
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		  
Parcels of undeveloped land 2bxp_ParcelsOfUndevelopedLand
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		  
540 Madison Venture LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties 540 Madison Avenue  
Ownership Percentage 60.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveFourZeroMadisonVentureLlcMember		  
Carrying value of the Company's investments in unconsolidated joint ventures 67,809us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveFourZeroMadisonVentureLlcMember		 [1]  
500 North Capitol LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties 500 North Capitol Street, NW  
Ownership Percentage 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveZeroZeroNorthCapitolLlcMember		  
Carrying value of the Company's investments in unconsolidated joint ventures (2,493)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveZeroZeroNorthCapitolLlcMember		 [1]  
Entity Owning Land And Infrastructure Of Project [Member]    
Schedule of Equity Method Investments [Line Items]    
Ownership Percentage 33.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_EntityOwningLandAndInfrastructureOfProjectMember		  
501 K Street [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties 1001 6th Street  
Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FivezerooneKStreetMember		 [5]  
Carrying value of the Company's investments in unconsolidated joint ventures 42,735us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FivezerooneKStreetMember		 [1]  
Potential additonal payments to joint venture partner 2bxp_Potentialadditonalpaymentstojointventurepartner
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FivezerooneKStreetMember		  
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) 520,000bxp_Minimumsquarefootagetomakeapotentialadditionalpaymenttojointventurepartnerinsqft
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FivezerooneKStreetMember		  
Podium Developer LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Properties North Station (Phase I - Air Rights)  
Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_PodiumDeveloperLLCMember		  
Carrying value of the Company's investments in unconsolidated joint ventures 5,576us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_PodiumDeveloperLLCMember		 [1]  
Unconsolidated Joint Ventures [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying value of the Company's investments in unconsolidated joint ventures (22,700)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_StatementEquityComponentsAxis
= bxp_UnconsolidatedJointVenturesMember		 (11,400)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_StatementEquityComponentsAxis
= bxp_UnconsolidatedJointVenturesMember
Unconsolidated Joint Ventures [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying value of the Company's investments in unconsolidated joint ventures $ 173,443us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= bxp_UnconsolidatedJointVenturesMember		 [1],[6] $ 182,042us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ dei_LegalEntityAxis
= bxp_UnconsolidatedJointVenturesMember		 [6]
[1] (1)Investments with deficit balances aggregating approximately $22.7 million have been reflected within Other Liabilities on the Company's Consolidated Balance Sheets.
[2] (2)The Company’s economic ownership has increased based on the achievement of certain return thresholds.
[3] (3)The Company’s wholly-owned entity that owns the office component of the project also owns a 33.3% interest in the entity owning the land, parking garage and infrastructure of the project.
[4] 4)The joint venture owns two in-service buildings, two buildings under construction and two undeveloped land parcels.
[5] Under the joint venture agreement, the partner will be entitled to up to two additional payments from the venture based on increases in total square footage of the project above 520,000 square feet and achieving certain project returns at stabilization.
[6] (2)Investments with deficit balances aggregating approximately $22.7 million and $11.4 million at March 31, 2015 and December 31, 2014, respectively, have been reflected within Other Liabilities on the Company's Consolidated Balance Sheets.