Accrued Interest Receivable Fair Value Disclosure

No definition available.

Name:	nrim_AccruedInterestReceivableFairValueDisclosure
Namespace Prefix:	nrim_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Loans And Loans Held For Sale Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	nrim_LoansAndLoansHeldForSaleFairValueDisclosure
Namespace Prefix:	nrim_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Purchased Receivables Fair Value Disclosure

+ References

No definition available.

+ Details

Name:	nrim_PurchasedReceivablesFairValueDisclosure
Namespace Prefix:	nrim_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of accrued expenses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

Name:	us-gaap_DepositsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

+ Details

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

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

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

- Definition

Fair value of obligations measured on a recurring basis.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

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

- Definition

Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

+ References

+ Details

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

- Definition

Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

+ Details

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

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

+ Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=nrim_MortgageServicingRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=nrim_CommercialServicingRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements - Schedule of Estimated Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	$ 274,441	$ 271,610
Total marketable equity securities	7,798	7,265
Purchased receivables, net	21,286	14,406
Mortgage servicing rights	11,254	10,821
Derivative liabilities	430	508
Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	514	853
Derivative liabilities	300	246
Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1,237	978
Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	130	262
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	88,331	74,549
Total marketable equity securities	7,798	7,265
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, due from banks and deposits in other banks	78,933	77,538
Investment securities available for sale, at fair value	88,331	74,549
Total marketable equity securities	7,798	7,265
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, due from banks and deposits in other banks	78,933	77,538
Investment securities available for sale, at fair value	88,331	74,549
Total marketable equity securities	7,798	7,265
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	186,110	197,061
Total marketable equity securities	0	0
Derivative liabilities	430	508
Significant Other Observable Inputs (Level 2) \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	514	853
Derivative liabilities	300	246
Significant Other Observable Inputs (Level 2) \| Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Significant Other Observable Inputs (Level 2) \| Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	130	262
Significant Other Observable Inputs (Level 2) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	186,110	197,061
Investment in Federal Home Loan Bank stock	2,071	2,101
Accrued interest receivable	5,010	4,817
Deposits	1,228,018	1,228,088
Securities sold under repurchase agreements	34,621	34,278
Borrowings	7,200	7,241
Accrued interest payable	57	22
Significant Other Observable Inputs (Level 2) \| Carrying Amount \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	514	853
Derivative liabilities	300	246
Significant Other Observable Inputs (Level 2) \| Carrying Amount \| Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	130	262
Significant Other Observable Inputs (Level 2) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	186,110	197,061
Investment in Federal Home Loan Bank stock	2,071	2,101
Accrued interest receivable	5,010	4,817
Deposits	1,227,692	1,227,086
Securities sold under repurchase agreements	34,621	34,278
Borrowings	7,098	6,965
Accrued interest payable	57	22
Significant Other Observable Inputs (Level 2) \| Fair Value \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	514	853
Derivative liabilities	300	246
Significant Other Observable Inputs (Level 2) \| Fair Value \| Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	130	262
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale, at fair value	0	0
Total marketable equity securities	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Interest rate swaps
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1,237	978
Significant Unobservable Inputs (Level 3) \| Retail interest rate contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Significant Unobservable Inputs (Level 3) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and loans held for sale	1,012,552	1,019,056
Purchased receivables, net	21,286	14,406
Junior subordinated debentures	10,310	10,310
Significant Unobservable Inputs (Level 3) \| Carrying Amount \| Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1,237	978
Significant Unobservable Inputs (Level 3) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and loans held for sale	994,382	995,115
Purchased receivables, net	21,286	14,406
Junior subordinated debentures	11,191	10,809
Significant Unobservable Inputs (Level 3) \| Fair Value \| Interest rate lock commitments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1,237	978
Mortgage servicing rights
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	11,254	10,821	$ 8,039	$ 7,305
Mortgage servicing rights \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	0	0
Mortgage servicing rights \| Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	0	0
Mortgage servicing rights \| Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	11,254	10,821
Mortgage servicing rights \| Significant Unobservable Inputs (Level 3) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	11,254	10,821
Mortgage servicing rights \| Significant Unobservable Inputs (Level 3) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	11,254	10,821
Commercial servicing rights
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	1,047	1,030
Commercial servicing rights \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	0	0
Commercial servicing rights \| Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	0	0
Commercial servicing rights \| Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	1,047	1,030
Commercial servicing rights \| Significant Unobservable Inputs (Level 3) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	1,047	1,030
Commercial servicing rights \| Significant Unobservable Inputs (Level 3) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage servicing rights	$ 1,047	$ 1,030