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Basis of Presentation and Significant Accounting Policies | 3 Months Ended
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Mar. 31, 2020
Basis of Presentation And Significant Accounting Policies |
Basis of Presentation and Significant Accounting Policies | Basis of Presentation, Significant Accounting Policies and Reclassifications Basis of Presentation The interim unaudited Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information and with instructions to Form 10-Q and Article 10 of Regulation S-X. The Consolidated Financial Statements include the accounts of Columbia Banking System, Inc. (“we”, “our”, “Columbia” or the “Company”) and its subsidiaries, including its wholly owned banking subsidiary Columbia State Bank (“Columbia Bank” or the “Bank”) and Columbia Trust Company (“Columbia Trust”). All intercompany transactions and accounts have been eliminated in consolidation. In the opinion of management, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair statement of the results for the interim periods presented have been included. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of results to be anticipated for the year ending December 31, 2020. The accompanying interim unaudited Consolidated Financial Statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2019 Annual Report on Form 10-K. Significant Accounting Policies The significant accounting policies used in preparation of our Consolidated Financial Statements are disclosed in our 2019 Annual Report on Form 10-K. In addition to the changes already disclosed in the Annual Report on Form 10-K regarding ASC 326, this ASC also made changes to the accounting for available for sale securities. One such change is to require credit losses to be presented as an allowance rather than a write-down on available for sale securities, which refers to securities management does not intend to sell or with respect to which management believes that it is more likely than not they will not be required to sell. With the exception of that change, there have not been any changes in our significant accounting policies compared to those contained in our 2019 Form 10-K disclosure for the year ended December 31, 2019. Reclassifications Certain amounts reported in prior periods have been reclassified in the Consolidated Financial Statements to conform to the current presentation. The reclassifications have no effect on net income or shareholders’ equity as previously reported.

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- Definition Basis Of Presentation And Significant Accounting Policies [Abstract] + References No definition available. + Details
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- Definition The entire disclosure for the basis of presentation and significant accounting policies concepts. Basis of presentation describes the underlying basis used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS). Accounting policies describe all significant accounting policies of the reporting entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369 + Details
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