Segment Information (Schedule Of Segment Reporting By Geographic Area And Property Type) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	$ 582,388bxp_RentalRevenueClassOffice	$ 539,906bxp_RentalRevenueClassOffice
Rental Revenue: Office/Technical	14,821bxp_RentalRevenueOfficeTechnical	15,697bxp_RentalRevenueOfficeTechnical
Rental Revenue: Residential	6,854bxp_RentalRevenueResidential	5,682bxp_RentalRevenueResidential
Rental Revenue: Hotel	9,085us-gaap_RevenueFromLeasedAndOwnedHotels	8,193us-gaap_RevenueFromLeasedAndOwnedHotels
Total revenue	613,148bxp_RentalRevenueTotal	569,478bxp_RentalRevenueTotal
Rental Revenue: % of Grand Totals	100.00%bxp_PercentageOfTotalRevenue	100.00%bxp_PercentageOfTotalRevenue
Rental Expenses: Class A Office	213,715bxp_RentalExpensesClassOffice	198,521bxp_RentalExpensesClassOffice
Rental Expenses: Office/Technical	4,089bxp_RentalExpensesOfficeTechnical	4,105bxp_RentalExpensesOfficeTechnical
Rental Expenses: Residential	3,546bxp_RentalExpensesResidential	3,762bxp_RentalExpensesResidential
Rental Expenses: Hotel	7,576us-gaap_DirectCostsOfHotels	6,797us-gaap_DirectCostsOfHotels
Rental Expenses: Total	228,926	213,185
Rental Expenses: % Of Grand Totals	100.00%bxp_PercentageOfTotalRentalExpenses	100.00%bxp_PercentageOfTotalRentalExpenses
Net operating Income	384,222	356,293
Net operating Income: % of Grand Totals	100.00%bxp_PercentageOfTotalNetOperatingIncome	100.00%bxp_PercentageOfTotalNetOperatingIncome
Boston [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	169,907	170,942
Rental Revenue: Office/Technical	6,120	5,820
Rental Revenue: Residential	1,178	1,163
Rental Revenue: Hotel	9,085	8,193
Total revenue	186,290	186,118
Rental Revenue: % of Grand Totals	30.38%	32.68%
Rental Expenses: Class A Office	74,465	71,398
Rental Expenses: Office/Technical	1,986	1,689
Rental Expenses: Residential	509	448
Rental Expenses: Hotel	7,576	6,797
Rental Expenses: Total	84,536	80,332
Rental Expenses: % Of Grand Totals	36.92%	37.68%
Net operating Income	101,754	105,786
Net operating Income: % of Grand Totals	26.48%	29.69%
New York [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	253,098	217,308
Rental Revenue: Office/Technical	0	0
Rental Revenue: Residential	0	0
Rental Revenue: Hotel	0	0
Total revenue	253,098	217,308
Rental Revenue: % of Grand Totals	41.28%	38.16%
Rental Expenses: Class A Office	85,061	74,371
Rental Expenses: Office/Technical	0	0
Rental Expenses: Residential	0	0
Rental Expenses: Hotel	0	0
Rental Expenses: Total	85,061	74,371
Rental Expenses: % Of Grand Totals	37.16%	34.89%
Net operating Income	168,037	142,937
Net operating Income: % of Grand Totals	43.73%	40.12%
San Francisco [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	66,252	54,608
Rental Revenue: Office/Technical	5,659	6,217
Rental Revenue: Residential	0	0
Rental Revenue: Hotel	0	0
Total revenue	71,911	60,825
Rental Revenue: % of Grand Totals	11.73%	10.68%
Rental Expenses: Class A Office	21,909	19,313
Rental Expenses: Office/Technical	912	1,214
Rental Expenses: Residential	0	0
Rental Expenses: Hotel	0	0
Rental Expenses: Total	22,821	20,527
Rental Expenses: % Of Grand Totals	9.97%	9.63%
Net operating Income	49,090	40,298
Net operating Income: % of Grand Totals	12.78%	11.31%
Washington, DC [Member]
Segment Reporting Information [Line Items]
Rental Revenue: Class A Office	93,131	97,048
Rental Revenue: Office/Technical	3,042	3,660
Rental Revenue: Residential	5,676	4,519
Rental Revenue: Hotel	0	0
Total revenue	101,849	105,227
Rental Revenue: % of Grand Totals	16.61%	18.48%
Rental Expenses: Class A Office	32,280	33,439
Rental Expenses: Office/Technical	1,191	1,202
Rental Expenses: Residential	3,037	3,314
Rental Expenses: Hotel	0	0
Rental Expenses: Total	36,508	37,955
Rental Expenses: % Of Grand Totals	15.95%	17.80%
Net operating Income	$ 65,341	$ 67,272
Net operating Income: % of Grand Totals	17.01%	18.88%