Business Combinations - Schedule of Loans Acquired with Deteriorating Credit Quality (Details) (USD $) In Thousands, unless otherwise specified	Apr. 02, 2014
Business Acquisition [Line Items]
Contractually required principal payments	$ 7,473
Nonaccretable difference	(3,654)
Fair value of purchased credit impaired loans	3,819
Alaska Pacific Bank
Business Acquisition [Line Items]
Contractually required principal payments	7,553
Nonaccretable difference	(3,654)
Fair value of purchased credit impaired loans	$ 3,899

Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition,Purchase Adjustment of Credit, Interest Rate, Liquidity and Nonaccretable Difference

No definition available.

+ Details

Name:	nrim_CertainLoansAcquiredinTransferNotAccountedforasDebtSecuritiesAcquiredDuringPeriodContractualCashFlowsNotExpectedtoBeCollectedNonAccretable
Namespace Prefix:	nrim_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Definition

Fair value at acquisition of acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Amount of contractually required payments receivable at acquisition of acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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