SUBSEQUENT EVENT Subsequent Event (Details) - Skagit Bank [Member] - USD ($) $ / shares in Units, $ in Millions	Jul. 25, 2018	Jun. 30, 2018
Subsequent Event [Line Items]
Business Combination, Consideration Transferred, Shares Issued for Each Aquiree Share	5.6664
Business Combination, Consideration Transferred, Value per share	$ 61.60
Business Combination, Consideration Transferred		$ 191
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		922
Business Combination, Acquired Receivable, Fair Value		599
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits		$ 811

Business Combination, Consideration Transferred, Shares Issued for Each Aquiree Share

No definition available.

Name:	banr_BusinessCombinationConsiderationTransferredSharesIssuedforEachAquireeShare
Namespace Prefix:	banr_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Business Combination, Consideration Transferred, Value per share

+ References

No definition available.

+ Details

Name:	banr_BusinessCombinationConsiderationTransferredValuepershare
Namespace Prefix:	banr_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Business Combination, Consideration to be Transferred, Aggregate Value

+ References

No definition available.

+ Details

Name:	banr_BusinessCombinationConsiderationtobeTransferredAggregateValue
Namespace Prefix:	banr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits

+ References

No definition available.

+ Details

Name:	banr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDeposits
Namespace Prefix:	banr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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

- Definition

Amount of assets acquired at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=banr_SkagitBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: