Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans (Details) $ in Thousands	Mar. 31, 2022 USD ($)
Receivables [Abstract]
Existing Troubled Debt Restructurings, Accrual Status	$ 2,978
New Troubled Debt Restructurings, Nonaccrual Status	7,062
Existing Troubled Debt Restructurings	$ 10,040

Financing Receivable, Troubled Debt Restructuring, Still Accruing, Existing Restructuring

No definition available.

Name:	nrim_FinancingReceivableTroubledDebtRestructuringStillAccruingExistingRestructuring
Namespace Prefix:	nrim_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant