Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]
Basis of Accounting, Policy [Policy Text Block]	Basis of presentation - The accompanying unaudited interim consolidated financial statements have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). Accordingly, they do not include all the information and footnotes required by U.S. Generally Accepted Accounting Principles ("GAAP") for complete financial statements. These unaudited interim consolidated financial statements should be read in conjunction with our audited consolidated financial statements and accompanying notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2025. In our opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the consolidated financial statements in accordance with GAAP have been included. Operating results for the three months ended March 31, 2026, are not necessarily indicative of the results that may be expected for future periods. In preparing the unaudited interim consolidated financial statements, we are required to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, and expenses. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to a determination of the allowance for credit losses ("ACL"), fair value of financial instruments and derivatives, and deferred tax assets and liabilities.
Consolidation, Policy [Policy Text Block]	Principles of consolidation - The accompanying consolidated financial statements include the accounts of First Northwest and its wholly owned subsidiary, First Fed. All material intercompany accounts and transactions have been eliminated in consolidation.
Subsequent Events, Policy [Policy Text Block]	Subsequent events - The Company has evaluated subsequent events for potential recognition and disclosure.
New Accounting Pronouncements, Policy [Policy Text Block]	*Recently issued accounting pronouncements not* yet adopted** In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. ASU 2024-03 requires additional disclosure of the nature of expenses included in the income statement in response to requests from investors for more information to better understand an entity's performance and potential future cash flows. The new standard requires disclosures about specific types of expenses included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. ASU 2024-03 is effective for the Company for fiscal years beginning after December 15, 2026, including interim periods within those fiscal years, with early adoption permitted. The adoption of this ASU is not expected to have a material impact on the consolidated financial statements and related disclosures. In September 2025, the FASB issued ASU 2025-06, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software which clarifies the accounting for costs related to internal-use software. The new guidance clarifies the threshold entities apply to begin capitalizing costs and removes all references to project stages in ASC Subtopic 350-40. ASU 2025-06 is effective for the Company for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years. The Company does not anticipate this ASU will have a material impact on its financial statements. In November 2025, the FASB issued ASU 2025-08, Financial instruments – Credit Losses (Topic 326): Purchased Loans, which amends the guidance in ASC 326 on the accounting for certain purchased loans. Under the ASU, entities must account for acquired loans (excluding credit cards) that meet certain criteria at acquisition ("purchased seasoned loans") by recognizing them at their purchase price plus an allowance for expected credit losses (the "gross-up approach"). ASU 2025-08 also introduces an accounting policy election related to the subsequent measurement of expected credit losses for entities that use a method other than a discounted cash flow analysis to estimate credit losses on purchased seasoned loans. If this accounting policy is elected, entities can use the amortized cost basis of the asset to subsequently measure their credit loss allowance. ASU 2025-08 is effective for annual reporting periods beginning after December 15, 2026, including interim periods within those fiscal years. Early adoption is permitted in an interim or annual reporting period in which financial statements have not yet been issued or made available for issuance. The Company is currently evaluating the impact of ASU 2025-08 on its consolidated financial statements.

Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2026

Basis of Accounting, Policy [Policy Text Block]

Basis of presentation - The accompanying unaudited interim consolidated financial statements have been prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission ("SEC"). Accordingly, they do not include all the information and footnotes required by U.S. Generally Accepted Accounting Principles ("GAAP") for complete financial statements. These unaudited interim consolidated financial statements should be read in conjunction with our audited consolidated financial statements and accompanying notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2025. In our opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of the consolidated financial statements in accordance with GAAP have been included. Operating results for the three months ended March 31, 2026, are not necessarily indicative of the results that may be expected for future periods.

In preparing the unaudited interim consolidated financial statements, we are required to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, and expenses. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change in the near term relate to a determination of the allowance for credit losses ("ACL"), fair value of financial instruments and derivatives, and deferred tax assets and liabilities.

Consolidation, Policy [Policy Text Block]

Principles of consolidation - The accompanying consolidated financial statements include the accounts of First Northwest and its wholly owned subsidiary, First Fed. All material intercompany accounts and transactions have been eliminated in consolidation.

Subsequent Events, Policy [Policy Text Block]

Subsequent events - The Company has evaluated subsequent events for potential recognition and disclosure.

New Accounting Pronouncements, Policy [Policy Text Block]

Recently issued accounting pronouncements not yet adopted

In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. ASU 2024-03 requires additional disclosure of the nature of expenses included in the income statement in response to requests from investors for more information to better understand an entity's performance and potential future cash flows. The new standard requires disclosures about specific types of expenses included in the expense captions presented on the face of the income statement as well as disclosures about selling expenses. ASU 2024-03 is effective for the Company for fiscal years beginning after December 15, 2026, including interim periods within those fiscal years, with early adoption permitted. The adoption of this ASU is not expected to have a material impact on the consolidated financial statements and related disclosures.

In September 2025, the FASB issued ASU 2025-06, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software which clarifies the accounting for costs related to internal-use software. The new guidance clarifies the threshold entities apply to begin capitalizing costs and removes all references to project stages in ASC Subtopic 350-40. ASU 2025-06 is effective for the Company for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years. The Company does not anticipate this ASU will have a material impact on its financial statements.

In November 2025, the FASB issued ASU 2025-08, Financial instruments – Credit Losses (Topic 326): Purchased Loans, which amends the guidance in ASC 326 on the accounting for certain purchased loans. Under the ASU, entities must account for acquired loans (excluding credit cards) that meet certain criteria at acquisition ("purchased seasoned loans") by recognizing them at their purchase price plus an allowance for expected credit losses (the "gross-up approach"). ASU 2025-08 also introduces an accounting policy election related to the subsequent measurement of expected credit losses for entities that use a method other than a discounted cash flow analysis to estimate credit losses on purchased seasoned loans. If this accounting policy is elected, entities can use the amortized cost basis of the asset to subsequently measure their credit loss allowance. ASU 2025-08 is effective for annual reporting periods beginning after December 15, 2026, including interim periods within those fiscal years. Early adoption is permitted in an interim or annual reporting period in which financial statements have not yet been issued or made available for issuance. The Company is currently evaluating the impact of ASU 2025-08 on its consolidated financial statements.