XML 70 R53.htm IDEA: XBRL DOCUMENT v3.10.0.1

Subsequent Events (Details)				6 Months Ended
	Jul. 27, 2018 USD ($) ft² yr	Jul. 19, 2018 USD ($) ft² a yr Buildings	Jul. 13, 2018 USD ($) ft²	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Aug. 07, 2018 ft² yr	Dec. 31, 2017 USD ($)
Subsequent Event [Line Items]
mortgage notes				$ 2,972,052,000			$ 2,979,281,000
Payments to Acquire Equity Method Investments				$ 65,250,000	$ 41,491,000
Three Hudson Boulevard [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage			25.00%
mortgage notes			$ 80,000,000
Debt Instrument, Basis Spread on Variable Rate			3.50%
Net Rentable Area (in sf) | ft²			2,000,000.0
Payments to Acquire Equity Method Investments			$ 45,600,000
Future payments to acquire equity method investments			$ 62,200,000
Santa Monica Business Park [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
mortgage notes		$ 300,000,000
Debt Instrument, Basis Spread on Variable Rate		1.28%
Derivative, Notional Amount		$ 300,000,000
Derivative, Average Fixed Interest Rate		4.063%
100 Causeway Street [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage	50.00%
Payment for improvements for equity method investment	$ 3,900,000
Net Rentable Area (in sf) | ft²	627,000
Term of Lease Signed (in years) | yr	20
Payments to Acquire Equity Method Investments	$ 37,400,000
Project estimated budget	$ 270,000,000
343 Madison Avenue [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) | ft²						900,000
Term of Lease Signed (in years) | yr						99
Ownership Percentage						55.00%
Santa Monica Business Park [Member] | Santa Monica Business Park [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Net purchase price		$ 627,500,000.0
seller funded leasing costs		$ 11,500,000
Area of Land | a		47
number of buildings | Buildings		21
Net Rentable Area (in sf) | ft²		1,200,000.0
rentable square feet subject to a ground lease (percetnage)		70.00%
Term of Lease Signed (in years) | yr		80
Payments to Acquire Equity Method Investments		$ 180,100,000
Joint venture partner [Member] | Santa Monica Business Park [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage		45.00%
Payments to Acquire Equity Method Investments		$ 147,400,000
Joint venture partner [Member] | 100 Causeway Street [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Ownership Percentage	50.00%
Payments to Acquire Equity Method Investments	$ 41,300,000

X

- Definition

Aggregate purchase price

+ References

No definition available.

+ Details

Name:	bxp_Aggregatepurchaseprice
Namespace Prefix:	bxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Future payments to acquire equity method investments

+ References

No definition available.

+ Details

Name:	bxp_Futurepaymentstoacquireequitymethodinvestments
Namespace Prefix:	bxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

number of buildings

+ References

No definition available.

+ Details

Name:	bxp_Numberofbuildings
Namespace Prefix:	bxp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Payment for improvements for equity method investment

+ References

No definition available.

+ Details

Name:	bxp_Paymentforimprovementsforequitymethodinvestment
Namespace Prefix:	bxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Project estimated budget

+ References

No definition available.

+ Details

Name:	bxp_Projectestimatedbudget
Namespace Prefix:	bxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

rentable square feet subject to a ground lease (percetnage)

+ References

No definition available.

+ Details

Name:	bxp_Rentablesquarefeetsubjecttoagroundleasepercetnage
Namespace Prefix:	bxp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

seller funded leasing costs

+ References

No definition available.

+ Details

Name:	bxp_Sellerfundedleasingcosts
Namespace Prefix:	bxp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Term of Lease Signed (in years)

+ References

No definition available.

+ Details

Name:	bxp_TermofLeaseSignedinyears
Namespace Prefix:	bxp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Area of land held.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfLand
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

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

X

- Definition

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bxp_ThreeHudsonBoulevardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bxp_SantaMonicaBusinessParkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bxp_OnehundredCausewayStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bxp_ThreeFourThreeMadisonAvenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BusinessAcquisitionAxis=bxp_SantaMonicaBusinessParkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=bxp_JointventurepartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: