STOCK REPURCHASES (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 26, 2014
Stock repurchases
Gain on repurchase of preferred stock	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 401	$ 2,070	$ 0	$ 0	$ 0	$ 0	$ 2,471
Common Stock [Member] | Banner Corporation Share Repurchase Plan [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased																978,826
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	978,826												978,826
Stock Repurchased During Period, Shares													0