Loans - Recorded investment in past due loans by loan segment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Aging of the recorded investment in past due loans by loan segment
Current	$ 2,193,023	$ 1,911,174
Nonaccrual	602	461
Totals	2,193,778	1,912,038
30-89 Days Past Due
Aging of the recorded investment in past due loans by loan segment
Past Due	153	403
Commercial
Aging of the recorded investment in past due loans by loan segment
Current	302,508	276,028
Nonaccrual	7	7
Totals	302,536	276,035
Commercial \| 30-89 Days Past Due
Aging of the recorded investment in past due loans by loan segment
Past Due	21
Paycheck Protection Program (PPP)
Aging of the recorded investment in past due loans by loan segment
Current	180,228
Totals	180,228
Construction and Land Development
Aging of the recorded investment in past due loans by loan segment
Current	191,604	196,600
Nonaccrual	164	176
Totals	191,768	196,776
HELOC and 1-4 Family Junior Mortgage
Aging of the recorded investment in past due loans by loan segment
Current	30,279	28,621
Totals	30,279	28,621
1st REM - 1-4 Family
Aging of the recorded investment in past due loans by loan segment
Current	39,532	36,671
Totals	39,532	36,671
LOCs and 2nd REM - Rentals
Aging of the recorded investment in past due loans by loan segment
Current	20,233	18,527
Nonaccrual	305	144
Totals	20,538	18,671
1st REM - Rentals
Aging of the recorded investment in past due loans by loan segment
Current	198,981	176,114
Nonaccrual	126	134
Totals	199,107	176,648
1st REM - Rentals \| 30-89 Days Past Due
Aging of the recorded investment in past due loans by loan segment
Past Due		400
Multifamily
Aging of the recorded investment in past due loans by loan segment
Current	522,491	515,014
Totals	522,491	515,014
CRE Owner Occupied
Aging of the recorded investment in past due loans by loan segment
Current	73,407	66,584
Totals	73,539	66,584
CRE Owner Occupied \| 30-89 Days Past Due
Aging of the recorded investment in past due loans by loan segment
Past Due	132
CRE Non-owner Occupied
Aging of the recorded investment in past due loans by loan segment
Current	627,651	592,545
Totals	627,651	592,545
Consumer and other
Aging of the recorded investment in past due loans by loan segment
Current	6,109	4,470
Totals	$ 6,109	4,473
Consumer and other \| 30-89 Days Past Due
Aging of the recorded investment in past due loans by loan segment
Past Due		$ 3

Amount of financing receivable not past due.

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

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

+ Details

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

- Definition

Amount of financing receivable past due.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922355-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919253-210447

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=bwb_FinancingReceivables30To89DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_PaycheckProtectionProgramPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_ConstructionAndLandDevelopmentPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_HomeEquityLineOfCreditAndOneToFourFamilyJuniorMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_OneToFourFamilyMortgageOneRealEstateMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_LineOfCreditAndRealEstateMortgageTwoRentalsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_RealEstateMortgageOneRentalsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_MultiFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bwb_CommercialRealEstateNonOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: