Mortgage Servicing Rights (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Servicing Assets at Fair Value [Line Items]
Serviced loans	$ 228,600,000nrim_ServicedLoans	$ 93,800,000nrim_ServicedLoans
Mortgage servicing rights	1,010,000us-gaap_ServicingAssetAtFairValueAmount
Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Serviced loans	96,500,000
Mortgage servicing rights
Servicing Assets at Fair Value [Line Items]
Servicing Asset at Fair Value, Additions	1,170,000
Servicing Asset at Fair Value, Changes in Fair Value Resulting from Changes in Valuation Inputs	(160,000)
Mortgage servicing rights	1,010,000
Other Noninterest Income
Servicing Assets at Fair Value [Line Items]
Fees and Commissions, Mortgage Servicing	$ 203,000

Fees and Commissions, Mortgage Servicing

No definition available.

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- Definition

Serviced Loans

+ References

No definition available.

+ Details

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- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

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- Definition

The net increase or decrease in fair value as a result of changes in the inputs used to calculate the fair value of servicing assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(4)(i)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

+ Details

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- Details

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- Details

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- Details

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- Details

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