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Basis of Presentation - Narrative (Details)
3 Months Ended
Mar. 31, 2015
Segment
Schedule of Equity Method Investments [Line Items]  
Number of segments 2us-gaap_NumberOfOperatingSegments
RML  
Schedule of Equity Method Investments [Line Items]  
Ownership Percentage 100.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
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= nrim_ResidentialMortgageHoldingCompanyLLCMember
NBG  
Schedule of Equity Method Investments [Line Items]  
Ownership Percentage 50.10%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= nrim_NorthrimBenefitsGroupMember