The percentage of cost of work charged for contract price.

No definition available.

Name:	bwb_ConstructionContractFeePercentFee
Namespace Prefix:	bwb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of credit risk associated with the commitment to extent the credit.

+ References

No definition available.

+ Details

Name:	bwb_CreditRiskOfCommitmentsToExtendCredit
Namespace Prefix:	bwb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of credit risk associated with the commitment letters of credit.

+ References

No definition available.

+ Details

Name:	bwb_CreditRiskOfLettersOfCredit
Namespace Prefix:	bwb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of credit risk associated with the unfunded commitments under lines of credit.

+ References

No definition available.

+ Details

Name:	bwb_CreditRiskOfUnfundedCommitmentsLinesOfCredit
Namespace Prefix:	bwb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_OtherCommitmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

+ Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=bwb_ContractWithThirdPartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_CapitalAdditionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_FederalHomeLoanBankAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments, Contingencies and Credit Risk (Details) - USD ($) $ in Thousands			12 Months Ended
	Dec. 03, 2019	Aug. 27, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments Outstanding
Unfunded Commitments Under Lines of Credit			$ 500,962	$ 395,032
Letters of Credit			79,225	81,053
Totals			580,187	476,085
Payment of construction costs			15,572	3,720	$ 1,235
Contract With Third Party
Commitments Outstanding
Commitment under contract	$ 6,321
Payment of construction costs			0
Construction of corporate headquarters office
Commitments Outstanding
Percentage of cost of work		3.75%
Commitment under contract		$ 23,000
Payment of construction costs			15,189
Federal Home Loan Bank Advances
Commitments Outstanding
Outstanding letters of credit			$ 108,502	$ 129,152