Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Receivables [Abstract]
Existing Troubled Debt Restructurings, Accrual Status	$ 291
Troubled Debt Restructurings, Accrual Status	291
New Troubled Debt Restructurings, Nonaccrual Status	4,844
Troubled Debt Restructurings, Nonaccrual Status	4,844
Existing Troubled Debt Restructurings	5,135
Troubled Debt Restructurings	$ 5,135	$ 10,600

Financing Receivable, Troubled Debt Restructuring, Existing Restructuring

No definition available.

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

- Definition

Financing Receivable, Troubled Debt Restructuring, Nonaccrual

+ References

No definition available.

+ Details

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

- Definition

Financing Receivable, Troubled Debt Restructuring, Nonaccrual, Existing Restructuring

+ References

No definition available.

+ Details

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

- Definition

Financing Receivable, Troubled Debt Restructuring, Still Accruing

+ References

No definition available.

+ Details

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

- Definition

Financing Receivable, Troubled Debt Restructuring, Still Accruing, Existing Restructuring

+ References

No definition available.

+ Details

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

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

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

- References

No definition available.

+ Details

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