Income Taxes - Components Of The Net Deferred Tax Asset (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Allowance for loan losses	$ 5,900	$ 6,543	$ 6,650
Loan fees, net of costs	1,871	1,653	1,411
Depreciation and amortization	(60)	446	537
Other real estate owned	50	174	1,381
Deferred compensation	1,691	1,665	1,973
Net operating loss carryforwards	589	0	0
Equity compensation	502	507	502
Loan discount	1,003nrim_DeferredTaxAssetLoanDiscount	0nrim_DeferredTaxAssetLoanDiscount	0nrim_DeferredTaxAssetLoanDiscount
Fair market value adjustment on certificates of deposit	321	0	0
Other	1,637us-gaap_DeferredTaxAssetsOther	1,122us-gaap_DeferredTaxAssetsOther	1,029us-gaap_DeferredTaxAssetsOther
Total Deferred Tax Asset	13,504us-gaap_DeferredTaxAssetsNet	12,110us-gaap_DeferredTaxAssetsNet	13,483us-gaap_DeferredTaxAssetsNet
Unrealized gain on available-for-sale investment securities	(173)	(451)	(955)
Intangible amortization	(2,206)	(1,949)	(1,807)
Other	(1,036)us-gaap_DeferredTaxLiabilitiesOther	(934)us-gaap_DeferredTaxLiabilitiesOther	(730)us-gaap_DeferredTaxLiabilitiesOther
Total Deferred Tax Liability	(3,415)us-gaap_DeferredTaxLiabilities	(3,334)us-gaap_DeferredTaxLiabilities	(3,492)us-gaap_DeferredTaxLiabilities
Net Deferred Tax Asset	$ 10,089us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 8,776us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 9,991us-gaap_DeferredTaxAssetsLiabilitiesNet

Deferred Tax Asset, Fair Value Adjustment on Certificates of Deposit

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Deferred Tax Asset, Loan Discount

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Deferred tax assets, depreciation and amortization.

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Deferred tax assets, loan fees, net of costs.

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Deferred Tax Assets Tax Deferred Expenses Related To Other Real Estate Owned

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Deferred tax liabilities, intangible amortization.

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Deferred tax liabilities, unrealized gains on available-for-sale securities.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from employee compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from the allowance for doubtful accounts.

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Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances.

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Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.

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