STOCK REPURCHASES (Details) - Common Stock [Member] - shares	12 Months Ended
	Dec. 31, 2016	Apr. 04, 2016
Stock repurchases
Stock surrendered during period, shares	25,628
Banner Corporation Share Repurchase Plan [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		1,711,540
Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding		5.00%
Stock trading plan, number of shares to be repurchased	1,300,000
Stock Repurchased During Period, Shares	1,145,250
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	566,290