Loans and Allowance for Credit Losses - Troubled Debt Restructured Loans (Details) $ in Thousands	Jun. 30, 2022 USD ($)
Receivables [Abstract]
Existing Troubled Debt Restructurings, Accrual Status	$ 3,008
New Troubled Debt Restructurings, Nonaccrual Status	5,844
Existing Troubled Debt Restructurings	$ 8,852

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