Basis of Presentation and Significant Accounting Policies	9 Months Ended
Sep. 30, 2017
Basis of Presentation And Significant Accounting Policies
Basis of Presentation and Significant Accounting Policies	Basis of Presentation, Significant Accounting Policies and Recent Developments 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 nine months ended September 30, 2017 are not necessarily indicative of results to be anticipated for the year ending December 31, 2017. The accompanying interim unaudited Consolidated Financial Statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2016 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 2016 Annual Report on Form 10-K. There have not been any changes in our significant accounting policies compared to those contained in our 2016 Form 10-K disclosure for the year ended December 31, 2016. Recent Developments In July 2017, we entered into an asset purchase agreement (the “Agreement”) with a third-party by which we sold our merchant card services portfolio. In addition, we transitioned our delivery of those services from in-house to an outsourced model to better serve our business clients via a broad selection of competitive, best-in-class payment processing solutions. The carrying amount of both assets and liabilities subject to the Agreement was zero. In the current quarter, we recorded a $14.0 million gain on sale of the merchant card services portfolio. Under the new business model, we share with the buyer in net merchant services revenue and no longer directly incur merchant processing expenses. Our net revenue share from merchant services is presented in “Card Revenue” in the Consolidated Statements of Income. For the third quarter of 2017, that net revenue share was $438 thousand.

Basis of Presentation, Significant Accounting Policies and Recent Developments

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 nine months ended September 30, 2017 are not necessarily indicative of results to be anticipated for the year ending December 31, 2017. The accompanying interim unaudited Consolidated Financial Statements should be read in conjunction with the financial statements and related notes contained in the Company’s 2016 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 2016 Annual Report on Form 10-K. There have not been any changes in our significant accounting policies compared to those contained in our 2016 Form 10-K disclosure for the year ended December 31, 2016.

Recent Developments

In July 2017, we entered into an asset purchase agreement (the “Agreement”) with a third-party by which we sold our merchant card services portfolio. In addition, we transitioned our delivery of those services from in-house to an outsourced model to better serve our business clients via a broad selection of competitive, best-in-class payment processing solutions. The carrying amount of both assets and liabilities subject to the Agreement was zero. In the current quarter, we recorded a $14.0 million gain on sale of the merchant card services portfolio. Under the new business model, we share with the buyer in net merchant services revenue and no longer directly incur merchant processing expenses. Our net revenue share from merchant services is presented in “Card Revenue” in the Consolidated Statements of Income. For the third quarter of 2017, that net revenue share was $438 thousand.