EMPLOYEE BENEFIT PLANS	12 Months Ended
Dec. 31, 2018
Retirement Benefits [Abstract]
EMPLOYEE BENEFIT PLANS	EMPLOYEE BENEFIT PLANS Employee Retirement Plans: Substantially all of the Company’s and the Banks' employees are eligible to participate in its 401(k)/Profit Sharing Plan, a defined contribution and profit sharing plan sponsored by the Company. Employees may elect to have a portion of their salary contributed to the plan in conformity with Section 401(k) of the Internal Revenue Code. At the discretion of the Company’s Board of Directors, the Company may elect to make matching and/or profit sharing contributions for the employees’ benefit. For the years ended December 31, 2018, 2017 and 2016, $5.4 million, $4.8 million and $4.6 million, respectively, was expensed for 401(k) contributions. The Board of Directors has elected to make a 4% of eligible compensation matching contribution for 2019. Supplemental Retirement and Salary Continuation Plans: Through the Banks, the Company is obligated under various non-qualified deferred compensation plans to help supplement the retirement income of certain executives, including certain retired executives, selected by resolution of the Banks’ Boards of Directors or in certain cases by the former directors of acquired banks. These plans are unfunded, include both defined benefit and defined contribution plans, and provide for payments after the executive’s retirement. In the event of a participant employee’s death prior to or during retirement, the Company is obligated to pay to the designated beneficiary the benefits set forth under the plan. For the years ended December 31, 2018, 2017 and 2016, expense recorded for supplemental retirement and salary continuation plan benefits totaled $2.3 million, $3.5 million, and $2.7 million, respectively. At December 31, 2018 and 2017, liabilities recorded for the various supplemental retirement and salary continuation plan benefits totaled $37.5 million and $38.6 million, respectively, and are recorded in a deferred compensation liability account. Deferred Compensation Plans and Rabbi Trusts: The Company and the Banks also offer non-qualified deferred compensation plans to members of their Boards of Directors and certain employees. The plans permit each participant to defer a portion of director fees, non-qualified retirement contributions, salary or bonuses for future receipt. Compensation is charged to expense in the period earned. In connection with its acquisitions, the Company also assumed liability for certain deferred compensation plans for key employees, retired employees and directors. In order to fund the plans’ future obligations, the Company has purchased life insurance policies or other investments, including Banner Corporation common stock, which in certain instances are held in irrevocable trusts commonly referred to as “Rabbi Trusts.” As the Company is the owner of the investments and the beneficiary of the insurance policies, and in order to reflect the Company’s policy to pay benefits equal to the accumulations, the assets and liabilities are reflected in the Consolidated Statements of Financial Condition. Banner Corporation common stock held for such plans is reported as a contra-equity account and was recorded at an original cost of $7.3 million at December 31, 2018 and $7.4 million at December 31, 2017. At December 31, 2018 and 2017, liabilities recorded in connection with deferred compensation plan benefits totaled $9.0 million ($7.3 million in contra-equity) and $9.9 million ($7.4 million in contra-equity), respectively, and are recorded in deferred compensation or equity as appropriate. The Banks have purchased, or acquired through mergers, life insurance policies in connection with the implementation of certain executive supplemental retirement, salary continuation and deferred compensation retirement plans, as well as additional policies not related to any specific plan. These policies provide protection against the adverse financial effects that could result from the death of a key employee and provide tax-exempt income to offset expenses associated with the plans. It is the Banks’ intent to hold these policies as a long-term investment. However, there will be an income tax impact if the Banks choose to surrender certain policies. Although the lives of individual current or former management-level employees are insured, the Banks are the owners and sole or partial beneficiaries. At December 31, 2018 and 2017, the cash surrender value of these policies was $177.5 million and $162.7 million, respectively. The Banks are exposed to credit risk to the extent an insurance company is unable to fulfill its financial obligations under a policy. In order to mitigate this risk, the Banks use a variety of insurance companies and regularly monitor their financial condition.

EMPLOYEE BENEFIT PLANS

Employee Retirement Plans: Substantially all of the Company’s and the Banks' employees are eligible to participate in its 401(k)/Profit Sharing Plan, a defined contribution and profit sharing plan sponsored by the Company. Employees may elect to have a portion of their salary contributed to the plan in conformity with Section 401(k) of the Internal Revenue Code. At the discretion of the Company’s Board of Directors, the Company may elect to make matching and/or profit sharing contributions for the employees’ benefit. For the years ended December 31, 2018, 2017 and 2016, $5.4 million, $4.8 million and $4.6 million, respectively, was expensed for 401(k) contributions. The Board of Directors has elected to make a 4% of eligible compensation matching contribution for 2019.

Supplemental Retirement and Salary Continuation Plans: Through the Banks, the Company is obligated under various non-qualified deferred compensation plans to help supplement the retirement income of certain executives, including certain retired executives, selected by resolution of the Banks’ Boards of Directors or in certain cases by the former directors of acquired banks. These plans are unfunded, include both defined benefit and defined contribution plans, and provide for payments after the executive’s retirement. In the event of a participant employee’s death prior to or during retirement, the Company is obligated to pay to the designated beneficiary the benefits set forth under the plan. For the years ended December 31, 2018, 2017 and 2016, expense recorded for supplemental retirement and salary continuation plan benefits totaled $2.3 million, $3.5 million, and $2.7 million, respectively. At December 31, 2018 and 2017, liabilities recorded for the various supplemental retirement and salary continuation plan benefits totaled $37.5 million and $38.6 million, respectively, and are recorded in a deferred compensation liability account.

Deferred Compensation Plans and Rabbi Trusts: The Company and the Banks also offer non-qualified deferred compensation plans to members of their Boards of Directors and certain employees. The plans permit each participant to defer a portion of director fees, non-qualified retirement contributions, salary or bonuses for future receipt. Compensation is charged to expense in the period earned. In connection with its acquisitions, the Company also assumed liability for certain deferred compensation plans for key employees, retired employees and directors.

In order to fund the plans’ future obligations, the Company has purchased life insurance policies or other investments, including Banner Corporation common stock, which in certain instances are held in irrevocable trusts commonly referred to as “Rabbi Trusts.” As the Company is the owner of the investments and the beneficiary of the insurance policies, and in order to reflect the Company’s policy to pay benefits equal to the accumulations, the assets and liabilities are reflected in the Consolidated Statements of Financial Condition. Banner Corporation common stock held for such plans is reported as a contra-equity account and was recorded at an original cost of $7.3 million at December 31, 2018 and $7.4 million at December 31, 2017. At December 31, 2018 and 2017, liabilities recorded in connection with deferred compensation plan benefits totaled $9.0 million ($7.3 million in contra-equity) and $9.9 million ($7.4 million in contra-equity), respectively, and are recorded in deferred compensation or equity as appropriate.

The Banks have purchased, or acquired through mergers, life insurance policies in connection with the implementation of certain executive supplemental retirement, salary continuation and deferred compensation retirement plans, as well as additional policies not related to any specific plan. These policies provide protection against the adverse financial effects that could result from the death of a key employee and provide tax-exempt income to offset expenses associated with the plans. It is the Banks’ intent to hold these policies as a long-term investment. However, there will be an income tax impact if the Banks choose to surrender certain policies. Although the lives of individual current or former management-level employees are insured, the Banks are the owners and sole or partial beneficiaries. At December 31, 2018 and 2017, the cash surrender value of these policies was $177.5 million and $162.7 million, respectively. The Banks are exposed to credit risk to the extent an insurance company is unable to fulfill its financial obligations under a policy. In order to mitigate this risk, the Banks use a variety of insurance companies and regularly monitor their financial condition.