Financing Receivable, Number Of Loans Modified

No definition available.

Name:	brkl_FinancingReceivableNumberOfLoansModified
Namespace Prefix:	brkl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Reduction in Interest Rate

+ References

No definition available.

+ Details

Name:	brkl_FinancingReceivableReductionInInterestRate
Namespace Prefix:	brkl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage, excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types: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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-34

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Period of payment deferral of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

+ Details

Name:	us-gaap_FinancingReceivableModifiedPaymentDeferralPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage, before modification, of weighted-average interest rate of financing receivable for debtor experiencing financial difficulty.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageInterestRateBeforeModification
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) in amortized cost of financing receivable modified for debtor experiencing financial difficulty.

+ References

+ Details

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringIncreaseDecreaseFromModification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=brkl_CommercialAndIndustrialRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	brkl_LoanModifiedAxis=brkl_LoanTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	brkl_LoanModifiedAxis=brkl_LoanTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	brkl_LoanModifiedAxis=brkl_LoanTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	brkl_LoanModifiedAxis=brkl_LoanTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityAndInterestRateReductionMember
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_LoanRestructuringModificationAxis=brkl_CombinationMaturityExtensionAndSignificantPaymentDelaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=brkl_CommercialRealEstateRelationshipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Allowance for Credit Losses - Schedule of Amortized Cost Basis of Loan Modifications Made to Borrowers Experiencing Financial Difficulty (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025 USD ($) loan	Jun. 30, 2024 USD ($) loan	Jun. 30, 2025 USD ($) loan	Jun. 30, 2024 USD ($) loan bank
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| loan	5	17	7	18
Amortized Cost	$ 4,625	$ 15,675	$ 5,716	$ 15,702
% of Total Class of Loans and Leases		0.65%		0.66%
Commercial And Industrial Relationships
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 0	$ 0	$ 0
Commercial And Industrial Relationships \| Maturity Extension:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| loan	2	1	4	2
Amortized Cost	$ 446	$ 104	$ 1,537	$ 131
% of Total Class of Loans and Leases	0.02%	0.00%	0.06%	0.01%
Term increase from modification		30 months
Commercial And Industrial Relationships \| Maturity Extension: \| Loan Tranche One
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification	12 months		15 months	30 months
Commercial And Industrial Relationships \| Maturity Extension: \| Loan Tranche Two
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification	7 months		12 months	13 months
Payment deferral period		2 months		2 months
Commercial And Industrial Relationships \| Maturity Extension: \| Loan Tranche Three
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification			7 months
Commercial And Industrial Relationships \| Maturity Extension: \| Loan Tranche Four
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification			3 months
Commercial And Industrial Relationships \| Significant Payment Delays:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans		12		12
Amortized Cost		$ 13,833		$ 13,833
% of Total Class of Loans and Leases		0.57%		0.57%
Payment deferral period		6 months		6 months
Increase from modification		$ 100		$ 100
Commercial And Industrial Relationships \| Combination - Maturity Extension and Interest Rate Reduction:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| loan	2	2	2	2
Amortized Cost	$ 364	$ 123	$ 364	$ 123
% of Total Class of Loans and Leases	0.01%	0.01%	0.01%	0.01%
Term increase from modification	36 months		36 months
Reduction in interest rate	2.30%
Interest rate before modification	2.30%	7.50%	2.30%	7.50%
Commercial And Industrial Relationships \| Combination - Maturity Extension and Interest Rate Reduction: \| Minimum
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification		21 months		21 months
Commercial And Industrial Relationships \| Combination - Maturity Extension and Interest Rate Reduction: \| Maximum
Financing Receivable, Troubled Debt Restructuring [Line Items]
Term increase from modification		25 months		25 months
Commercial And Industrial Relationships \| Combination - Maturity Extension and Significant Payment Delays:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| loan		2		2
Amortized Cost		$ 1,615		$ 1,615
% of Total Class of Loans and Leases		0.07%		0.07%
Term increase from modification		6 months		6 months
Commercial Real Estate Relationship \| Significant Payment Delays:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| loan	1		1
Amortized Cost	$ 3,815		$ 3,815
% of Total Class of Loans and Leases	0.07%		0.07%
Payment deferral period	12 months		12 months