Mortgage loans interest rate for remainder of fiscal year.

No definition available.

Name:	bdn_MortgageLoansInterestRateForRemainderOfFiscalYear
Namespace Prefix:	bdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Mortgage loans interest rate for year two and thereafter.

+ References

No definition available.

+ Details

Name:	bdn_MortgageLoansInterestRateForYearTwoAndThereafter
Namespace Prefix:	bdn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Mortgage loans maturity date, month and year.

+ References

No definition available.

+ Details

Name:	bdn_MortgageLoansMaturityDateMonthAndYear
Namespace Prefix:	bdn_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Notes receivable final payment.

+ References

No definition available.

+ Details

Name:	bdn_NotesReceivableFinalPayment
Namespace Prefix:	bdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

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

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

- Definition

Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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

- Definition

Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	srt_CounterpartyNameAxis=bdn_ThirdPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bdn_BrandywineNineteenNineteenVenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value of Financial Instruments (Textual) (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2018	Jun. 26, 2018
Third Party [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable		$ 3.4
Mortgage loans, interest rate for remainder of 2018		7.00%
Mortgage loans, interest rate after 2018 until maturity date in March of 2020		8.00%
Mortgage loans, maturity date		2020-03
Third Party [Member] \| Scenario Forecast [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amount expected to be received from note receivable	$ 3.1
Brandywine 1919 Ventures [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Mortgage loan			$ 44.4
Equity method investment, ownership percentage			50.00%
Brandywine 1919 Ventures [Member] \| Other Assets [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable			$ 44.4