BASIS OF PRESENTATION AND CRITICAL ACCOUNTING POLICIES (Policies)	6 Months Ended
Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	The accompanying unaudited consolidated interim financial statements include the accounts of Banner Corporation (the Company or Banner), a bank holding company incorporated in the State of Washington and its wholly-owned subsidiaries, Banner Bank and Islanders Bank (the Banks). These unaudited consolidated interim financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission (SEC). In preparing these condensed consolidated financial statements, the Company has evaluated events and transactions subsequent to June 30, 2015 for potential recognition or disclosure. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. Certain information and disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. Certain reclassifications have been made to the 2014 Consolidated Financial Statements and/or schedules to conform to the 2015 presentation. These reclassifications may have affected certain ratios for the prior periods. The effect of these reclassifications is considered immaterial. All significant intercompany transactions and balances have been eliminated. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements. Various elements of the Company’s accounting policies, by their nature, are inherently subject to estimation techniques, valuation assumptions and other subjective assessments. In particular, management has identified several accounting policies that, due to the judgments, estimates and assumptions inherent in those policies, are critical to an understanding of Banner’s financial statements. These policies relate to (i) the methodology for the recognition of interest income, (ii) determination of the provision and allowance for loan and lease losses, (iii) the valuation of financial assets and liabilities recorded at fair value, including other-than-temporary impairment (OTTI) losses, (iv) the valuation of intangibles, such as goodwill, core deposit intangibles and mortgage servicing rights, (v) the valuation of or recognition of deferred tax assets and liabilities, and (vi) the application of acquisition accounting standards to business combinations including purchased credit-impaired loans. These policies and judgments, estimates and assumptions are described in greater detail in subsequent notes to the Consolidated Financial Statements and Management’s Discussion and Analysis of Financial Condition and Results of Operations (Critical Accounting Policies) in our Annual Report on Form 10-K for the year ended December 31, 2014 filed with the SEC. There have been no significant changes in our application of accounting policies during the first six months of 2015. The information included in this Form 10-Q should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2014 as filed with the SEC (2014 Form 10-K). Interim results are not necessarily indicative of results for a full year or any other interim period.

The accompanying unaudited consolidated interim financial statements include the accounts of Banner Corporation (the Company or Banner), a bank holding company incorporated in the State of Washington and its wholly-owned subsidiaries, Banner Bank and Islanders Bank (the Banks).

These unaudited consolidated interim financial statements have been prepared in accordance with accounting principles generally accepted in the United States (GAAP) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X as promulgated by the Securities and Exchange Commission (SEC). In preparing these condensed consolidated financial statements, the Company has evaluated events and transactions subsequent to June 30, 2015 for potential recognition or disclosure. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. Certain information and disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. Certain reclassifications have been made to the 2014 Consolidated Financial Statements and/or schedules to conform to the 2015 presentation. These reclassifications may have affected certain ratios for the prior periods. The effect of these reclassifications is considered immaterial. All significant intercompany transactions and balances have been eliminated.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements. Various elements of the Company’s accounting policies, by their nature, are inherently subject to estimation techniques, valuation assumptions and other subjective assessments. In particular, management has identified several accounting policies that, due to the judgments, estimates and assumptions inherent in those policies, are critical to an understanding of Banner’s financial statements. These policies relate to (i) the methodology for the recognition of interest income, (ii) determination of the provision and allowance for loan and lease losses, (iii) the valuation of financial assets and liabilities recorded at fair value, including other-than-temporary impairment (OTTI) losses, (iv) the valuation of intangibles, such as goodwill, core deposit intangibles and mortgage servicing rights, (v) the valuation of or recognition of deferred tax assets and liabilities, and (vi) the application of acquisition accounting standards to business combinations including purchased credit-impaired loans. These policies and judgments, estimates and assumptions are described in greater detail in subsequent notes to the Consolidated Financial Statements and Management’s Discussion and Analysis of Financial Condition and Results of Operations (Critical Accounting Policies) in our Annual Report on Form 10-K for the year ended December 31, 2014 filed with the SEC. There have been no significant changes in our application of accounting policies during the first six months of 2015.

The information included in this Form 10-Q should be read in conjunction with our Annual Report on Form 10-K for the year ended December 31, 2014 as filed with the SEC (2014 Form 10-K). Interim results are not necessarily indicative of results for a full year or any other interim period.