Debt instrument additional basis spread.

No definition available.

Name:	bdn_DebtInstrumentAdditionalBasisSpread
Namespace Prefix:	bdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, maturity extension period.

+ References

No definition available.

+ Details

Name:	bdn_DebtInstrumentMaturityExtensionPeriod
Namespace Prefix:	bdn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, number of extensions.

+ References

No definition available.

+ Details

Name:	bdn_DebtInstrumentNumberOfExtensions
Namespace Prefix:	bdn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, maximum leverage ratio.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMaximumLeverageRatio
Namespace Prefix:	bdn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, maximum percent of payments of dividends and distributions.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMaximumPercentOfPaymentsOfDividendsAndDistributions
Namespace Prefix:	bdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, maximum secured indebtedness to asset value ratio.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMaximumSecuredIndebtednessToAssetValueRatio
Namespace Prefix:	bdn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, maximum unsecured indebtedness to unencumbered asset value ratio.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMaximumUnsecuredIndebtednessToUnencumberedAssetValueRatio
Namespace Prefix:	bdn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, minimum fixed charge coverage ratio.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMinimumFixedChargeCoverageRatio
Namespace Prefix:	bdn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, covenant, minimum unencumbered cash flow to interest expense on unsecured debt ratio.

+ References

No definition available.

+ Details

Name:	bdn_LineOfCreditFacilityCovenantMinimumUnencumberedCashFlowToInterestExpenseOnUnsecuredDebtRatio
Namespace Prefix:	bdn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- 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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

Name:	us-gaap_DeferredFinanceCostsNoncurrentGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=bdn_PriorRevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_FederalFundsEffectiveSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=bdn_LondonInterbankOfferedRateOneMonthPeriodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bdn_NewCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
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Period Type:

Debt Obligations (Textual) (Details)		9 Months Ended
Debt Obligations (Textual) (Details)	Jul. 17, 2018 USD ($) Extension	Sep. 30, 2018 USD ($)	Dec. 31, 2017	Sep. 30, 2017 USD ($)
Prior Revolving Credit Facilty [Member]
Debt Instrument [Line Items]
Debt instrument maturity date	May 15, 2019	May 15, 2019
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate				2.34%
Commitment fee percentage		0.25%
Minimum fixed charge coverage ratio		1.5
Maximum leverage ratio		0.60
Maximum unsecured indebtedness to unencumbered asset value ratio		0.60
Maximum secured indebtedness to total asset value ratio		0.40
Minimum unencumbered cash flow to interest expense on unsecured debt ratio		1.75
Maximum percent of payments of dividends and distributions		95.00%
Line of Credit		$ 0		$ 178,000,000.0
Letters of credit outstanding amount				$ 13,500,000
Effective interest rate on credit facility				2.43%
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Commitment fee percentage		0.125%
Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage		0.30%
Revolving Credit Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.10%
Revolving Credit Facility [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.775%
Revolving Credit Facility [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.45%
Revolving Credit Facility [Member] \| Federal Funds Rate [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.50%
Revolving Credit Facility [Member] \| LIBOR for a One Month Period [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.00%
Revolving Credit Facility [Member] \| LIBOR for a One Month Period [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Credit Spread on a LIBOR Rate Loan		0.00%
Revolving Credit Facility [Member] \| LIBOR for a One Month Period [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Credit Spread on a LIBOR Rate Loan		0.45%
Revolving Credit Facility [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 600,000,000.0
Debt instrument maturity date	Jul. 15, 2022
Debt instrument, maturity extension period	6 months
Debt instrument, number of extensions \| Extension	2
Debt financing costs	$ 2,700,000
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate		4.05%	4.04%