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Loans and Allowance for Credit Losses - Analysis Of Loan Transactions (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Loans and Leases Receivable, Related Parties [Roll Forward] |  |  |
Balance, beginning of the year | $ 217 | $ 309 | $ 0
Loans made | 0 | 0 | 309
Repayments | 26 | 92 | 0
Balance, end of year | $ 191 | $ 217 | $ 309

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- Definition Analysis Of Loan Transactions + References No definition available. + Details
Name: | nrim_AnalysisOfLoanTransactions
Namespace Prefix: | nrim_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Analysis Of Loan Transactions Loans Made + References No definition available. + Details
Name: | nrim_AnalysisOfLoanTransactionsLoansMade
Namespace Prefix: | nrim_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Analysis Of Loan Transactions Repayment Of Loans + References No definition available. + Details
Name: | nrim_AnalysisOfLoanTransactionsRepaymentOfLoans
Namespace Prefix: | nrim_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_LoansAndLeasesReceivableRelatedPartiesRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration