Loans - Narrative (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 02, 2014
Loans [Abstract]
Loans secured by real estate	74.00%
Loans secured for general commercial uses	26.00%
Nonaccrual loans	$ 4,674,000	$ 1,815,000
Interest income earned on nonaccrual loans	218,000	188,000	453,000
Interest Income Earned on Nonaccrual Loans With No Balance	350,000	250,000	344,000
Nonperforming loans minimum threshold for individual impairment evaluation	50,000
Recorded investment in loans considered to be impaired	11,298,000	8,751,000
Fair value of purchased credit impaired loans	3,000,000			3,900,000
Loans classified as troubled debt restructuring	7,688,000	7,900,000
Commitment to Lend	0
Write down on TDR	0	0
TDR With Specific Impairment Total Recorded Investment	0	0
Recorded investment classified as nonaccrual loans		2,200,000
TDR's not included in nonaccrual		923,000
Loans Pledged as Collateral	0us-gaap_LoansPledgedAsCollateral	0us-gaap_LoansPledgedAsCollateral
Serviced loans	228,600,000nrim_ServicedLoans	93,800,000nrim_ServicedLoans
Amounts held in escrow	1,300,000us-gaap_EscrowDeposit	714,000us-gaap_EscrowDeposit
Unfunded loan commitments	$ 0	$ 0

Financing Receivable Recorded Investment Interest Income Earned On Nonaccrual Loans

No definition available.

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- Definition

Financing Receivables Modifications Recorded Investment Classified As Nonaccrual Loans

+ References

No definition available.

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- Definition

Financing Receivables Percentage Of Total Loans Secured By Real Estate

+ References

No definition available.

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- Definition

Financing Receivables Percentage Of Total Loans Secured For General Commercial Uses

+ References

No definition available.

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- Definition

Financing receivables unfunded loan commitments to directors and officers.

+ References

No definition available.

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- Definition

Interest Income Earned on Nonaccrual Loans With No Balance

+ References

No definition available.

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- Definition

Nonperforming loans minimum threshold for individual impairment evaluation.

+ References

No definition available.

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- Definition

Serviced Loans

+ References

No definition available.

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- Definition

Troubled Debt Restructurings Still Accruing Interest

+ References

No definition available.

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- Definition

Troubled Debt Restructurings with a specific impairment, total recorded investment.

+ References

No definition available.

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- 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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

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- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10)

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

+ Details

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

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- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524

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-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 45

-Paragraph 1

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