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Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Apr. 10, 2014
sqft
Schedule of Equity Method Investments [Line Items]      
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures $ 193,394us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 140,097us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures  
Investments In Affiliates Subsidiaries Associates And Joint Ventures, net 182,042bxp_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVenturesnet [1]    
Unconsolidated Joint Ventures [Member]      
Schedule of Equity Method Investments [Line Items]      
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures (11,400)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_UnconsolidatedJointVenturesMember		 (14,000)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_UnconsolidatedJointVenturesMember		  
Square 407 Limited Partnership      
Schedule of Equity Method Investments [Line Items]      
Properties Market Square North    
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_SquareFourZeroSevenLimitedPartnershipMember		    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures (8,022)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_SquareFourZeroSevenLimitedPartnershipMember		 [1]    
The Metropolitan Square Associates LLC      
Schedule of Equity Method Investments [Line Items]      
Properties Metropolitan Square    
Equity Method Investment, Ownership Percentage 51.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_MetropolitanSquareAssociatesLlcMember		    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures 8,539us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_MetropolitanSquareAssociatesLlcMember		    
BP/CRF 901 New York Avenue LLC      
Schedule of Equity Method Investments [Line Items]      
Properties 901 New York Avenue    
Equity Method Investment, Ownership Percentage 25.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_BpCrfNineZeroOneNewYorkAvenueLlcMember		 [2]    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures (1,080)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_BpCrfNineZeroOneNewYorkAvenueLlcMember		 [1]    
WP Project Developer LLC      
Schedule of Equity Method Investments [Line Items]      
Properties Wisconsin Place Land and Infrastructure    
Equity Method Investment, Ownership Percentage 33.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_WpProjectDeveloperLlcMember		 [3]    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures 45,514us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_WpProjectDeveloperLlcMember		    
Annapolis Junction NFM, LLC      
Schedule of Equity Method Investments [Line Items]      
Properties Annapolis Junction    
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		 [4]    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures 25,246us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_AnnapolisJunctionNfmLlcMember		    
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      
Schedule of Equity Method Investments [Line Items]      
Properties 540 Madison Avenue    
Equity Method Investment, Ownership Percentage 60.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveFourZeroMadisonVentureLlcMember		    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures 68,128us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveFourZeroMadisonVentureLlcMember		    
500 North Capitol LLC      
Schedule of Equity Method Investments [Line Items]      
Properties 500 North Capitol Street, NW    
Equity Method Investment, Ownership Percentage 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveZeroZeroNorthCapitolLlcMember		    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures (2,250)us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_FiveZeroZeroNorthCapitolLlcMember		 [1]    
1001 6th Street (formerly five zero one K Street ) [Member]      
Schedule of Equity Method Investments [Line Items]      
Properties 1001 6th Street formerly 501 K Street)    
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_OneZeroZeroONesixthStreetformerlyfivezerooneKStreetMember		 [5]    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures 41,736us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_OneZeroZeroONesixthStreetformerlyfivezerooneKStreetMember		    
Potential additonal payments to joint venture partner 2bxp_Potentialadditonalpaymentstojointventurepartner
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_OneZeroZeroONesixthStreetformerlyfivezerooneKStreetMember		    
Minimum square footage to make a potential additional payment to joint venture partner (in sqft) 520,000bxp_Minimumsquarefootagetomakeapotentialadditionalpaymenttojointventurepartnerinsqft
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_OneZeroZeroONesixthStreetformerlyfivezerooneKStreetMember		   520,000bxp_Minimumsquarefootagetomakeapotentialadditionalpaymenttojointventurepartnerinsqft
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_OneZeroZeroONesixthStreetformerlyfivezerooneKStreetMember
Entity Owning Land And Infrastructure Of Project [Member]      
Schedule of Equity Method Investments [Line Items]      
Equity Method Investment, Ownership Percentage 33.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_EntityOwningLandAndInfrastructureOfProjectMember		    
Podium Developer LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Properties North Station (Phase I - Air Rights)    
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_PodiumDeveloperLLCMember		    
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures $ 4,231us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= bxp_PodiumDeveloperLLCMember		    
[1] Investments with deficit balances aggregating approximately $11.4 million have been reflected within Other Liabilities on the Company's Consolidated Balance Sheets.
[2] The Company’s economic ownership has increased based on the achievement of certain return thresholds.
[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] 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.