Basis of Presentation and Significant Accounting Policies	9 Months Ended
Sep. 30, 2014
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, 2014 are not necessarily indicative of results to be anticipated for the year ending December 31, 2014. The accompanying interim unaudited consolidated financial statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2013 Annual Report on Form 10-K. Due to the timing of the acquisition of West Coast Bancorp (“West Coast”), our results of operations for the nine month period ended September 30, 2014 include the acquisition for the entire nine month period, however the prior year period only includes the acquisition for six months of the nine month period. 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 2013 Annual Report on Form 10-K. There have not been any changes in our significant accounting policies compared to those contained in our 2013 Form 10-K disclosure for the year ended December 31, 2013. Correction of Immaterial Error Related to Prior Periods During the three months ended September 30, 2014, the Company made a $2.6 million adjustment which increased interest income on taxable securities as a result of identifying that the premium amortization related to the Company’s mortgage-backed securities, as calculated by a third-party provider, was not being amortized utilizing an acceptable method under accounting principles generally accepted in the United States. The adjustment reflects the one-time correction necessary to change the accounting for premium amortization to be in conformity with the interest method. Based upon an evaluation of all relevant factors, management believes the correcting adjustment did not have a material impact on the Company’s current quarter, current year-to-date, or previously reported results.

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, 2014 are not necessarily indicative of results to be anticipated for the year ending December 31, 2014. The accompanying interim unaudited consolidated financial statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2013 Annual Report on Form 10-K.

Due to the timing of the acquisition of West Coast Bancorp (“West Coast”), our results of operations for the nine month period ended September 30, 2014 include the acquisition for the entire nine month period, however the prior year period only includes the acquisition for six months of the nine month period. 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 2013 Annual Report on Form 10-K. There have not been any changes in our significant accounting policies compared to those contained in our 2013 Form 10-K disclosure for the year ended December 31, 2013.

Correction of Immaterial Error Related to Prior Periods

During the three months ended September 30, 2014, the Company made a $2.6 million adjustment which increased interest income on taxable securities as a result of identifying that the premium amortization related to the Company’s mortgage-backed securities, as calculated by a third-party provider, was not being amortized utilizing an acceptable method under accounting principles generally accepted in the United States. The adjustment reflects the one-time correction necessary to change the accounting for premium amortization to be in conformity with the interest method. Based upon an evaluation of all relevant factors, management believes the correcting adjustment did not have a material impact on the Company’s current quarter, current year-to-date, or previously reported results.