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Significant Accounting Policies (Policies) | 6 Months Ended
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Jun. 30, 2025
Accounting Policies [Abstract] |
Organization And Nature Of Business | The accounting and financial reporting policies of Columbia Banking System, Inc. conform to accounting principles generally accepted in the United States of America and with prevailing practices within the banking and securities industries. All references in this report to "Columbia," "we," "our," or "us" or similar references mean the Company and its subsidiaries, including the wholly-owned banking subsidiary Columbia Bank (dba: Umpqua Bank) (the "Bank"). In order to align with the name of the holding company and the variety of brands already operated by the Bank today under the Columbia name, the Company renamed the Bank to "Columbia Bank" effective July 1, 2025, and the Bank will begin doing business under the Columbia Bank name and brand beginning on September 1, 2025. FinPac is a commercial equipment leasing company and a wholly-owned subsidiary of the Bank. The accompanying interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, and the Bank's wholly-owned subsidiaries. All inter-company balances and transactions have been eliminated. The condensed consolidated financial statements have not been audited. A more detailed description of the Company's accounting and financial reporting policies is included in the Company's Annual Report on Form 10-K for the year ended December 31, 2024. These interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Company's Annual Report on Form 10-K for the year ended December 31, 2024. In preparing these condensed consolidated financial statements, the Company has evaluated events and transactions subsequent to June 30, 2025, for potential recognition or disclosure. In management's opinion, all accounting adjustments necessary to accurately reflect the financial position and results of operations on the accompanying financial statements have been made. These adjustments include those that are normal and recurring in nature considered necessary for a fair presentation. The results for interim periods are not necessarily indicative of results for the full year or any other interim period.
Application of new accounting guidance and Recent accounting pronouncements | Application of New Accounting Guidance
Standard |  | Description |  | Effective Date |  | Effect on the Financial Statements or Other Significant Matters
ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures |  | The amendments are intended to provide more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information. The ASU requires annual disclosure of the rate reconciliation of specific categories as well as additional information related to the reconciliation of certain items that meet a quantitative threshold and further disaggregation of income taxes paid. |  | Fiscal years beginning after December 15, 2024. |  | The Company adopted the guidance on January 1, 2025 for annual reporting purposes. Refined disclosures will be included in the 2025 10-K.
Significant Accounting Standards Issued but Not Yet Adopted
Standard |  | Description |  | Effective Date |  | Effect on the Financial Statements or Other Significant Matters
ASU No. 2024-03 Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses |  | These amendments are aimed to enhance the transparency and usefulness of financial information by requiring entities to break down significant expense categories in the notes to the financial statements. The amendments focus on the disaggregation of income statement expenses and specifically address the need for more detailed disclosures about expense categories. |  | Fiscal years beginning after December 15, 2026, and for interim periods beginning after December 15, 2027. Early adoption is permitted. |  | The Company is currently evaluating the impact of this ASU on the Company's consolidated financial statements.

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- Definition Organization And Nature Of Business + References No definition available. + Details
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- Definition Disclosure of accounting policy pertaining to new accounting pronouncements that may impact the entity's financial reporting. Includes, but is not limited to, quantification of the expected or actual impact. + References No definition available. + Details
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