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Basis of Presentation and Significant Accounting Policies | 9 Months Ended
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Sep. 30, 2015
Basis of Presentation And Significant Accounting Policies |
Basis of Presentation and Significant Accounting Policies | Basis of Presentation and Significant Accounting Policies 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 West Coast Trust Company, Inc. (“West Coast 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 nine months ended September 30, 2015 are not necessarily indicative of results to be anticipated for the year ending December 31, 2015. The accompanying interim unaudited consolidated financial statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2014 Annual Report on Form 10-K. Our results of operations for the three and nine month periods ended September 30, 2015 include the acquisition of Intermountain Community Bancorp (“Intermountain”) for the entire period. However, the results of operations for the prior year periods do not include the acquisition. See Note 3, Business Combinations, for further information regarding this acquisition. Significant Accounting Policies The significant accounting policies used in preparation of our consolidated financial statements are disclosed in our 2014 Annual Report on Form 10-K. There have not been any changes in our significant accounting policies compared to those contained in our 2014 Form 10-K disclosure for the year ended December 31, 2014.

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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 No definition available. + Details
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