STOCK REPURCHASES (Details) - Common Stock [Member] - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stock repurchases
Stock surrendered during period, shares	27,653	29,579
Banner Corporation 2017 Share Repurchase Authorization [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		1,658,245
Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding		5.00%
Stock Repurchased During Period, Shares		545,166
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased		1,113,079
Banner Corporation 2018 Share Repurchase Authorization [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	1,621,549
Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding	5.00%
Stock Repurchased During Period, Shares	594,711
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	1,296,549
Banner Corporation 2018 Share Repurchases, 2017 Authorization [Member]
Stock repurchases
Stock Repurchased During Period, Shares	269,711
Banner Corporation 2018 Share Repurchases, 2018 Authorization [Member]
Stock repurchases
Stock Repurchased During Period, Shares	325,000

Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding

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- Definition

Stock surrendered during period, shares by employees to satisfy tax withholding obligations upon vesting of restricted stock grants

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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- Definition

The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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