DERIVATIVES AND HEDGING (Derivatives Not Designated as Hedging, by Balance Sheet Location) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 5,682	$ 5,083
Liability Derivatives, Fair Value	5,682	5,083
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	5,682	5,083
Liability Derivatives, Fair Value	5,682	5,083
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	351,043	357,855
Liability Derivatives, Notional/Contract Amount	389,232	345,810
Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	5,877	5,159
Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	5,792	4,837
Not Designated as Hedging Instrument [Member] \| Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	286,390	285,047
Liability Derivatives, Notional/Contract Amount	286,390	285,047
Not Designated as Hedging Instrument [Member] \| Interest rate swaps [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	5,376	4,636
Not Designated as Hedging Instrument [Member] \| Interest rate swaps [Member] \| Loans Receivable [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	312	499
Not Designated as Hedging Instrument [Member] \| Interest rate swaps [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	5,376	4,636
Not Designated as Hedging Instrument [Member] \| Mortgage loan commitments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	41,655	29,739
Liability Derivatives, Notional/Contract Amount	22,401	13,763
Not Designated as Hedging Instrument [Member] \| Mortgage loan commitments [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	389	225
Not Designated as Hedging Instrument [Member] \| Mortgage loan commitments [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	105	153
Not Designated as Hedging Instrument [Member] \| Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	22,998	43,069
Liability Derivatives, Notional/Contract Amount	80,441	47,000
Not Designated as Hedging Instrument [Member] \| Forward Contracts [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	112	298
Not Designated as Hedging Instrument [Member] \| Forward Contracts [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	$ 311	$ 48

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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

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- Details

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- Details

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- Details

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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
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Data Type:	na
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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_LoansReceivableMember
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Data Type:	na
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=banr_MortgageLoanCommitmentsMember
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Data Type:	na
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- Details

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