BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
INTEREST INCOME:
Interest-bearing deposits	$ 97,171	$ 93,708	$ 93,148	$ 91,043	$ 92,099	$ 52,188	$ 51,457	$ 46,536	$ 46,661	$ 47,064	$ 43,808	$ 42,339	$ 375,069	$ 242,279	$ 179,872
OTHER INCOME (EXPENSE):
Other income													6,001	2,821	1,885
Other expenses													(30,131)	(17,565)	(13,619)
Income before provision for income taxes	34,747	36,128	31,798	26,968	10,201	19,589	19,864	18,318	17,544	22,105	25,683	15,790	129,640	67,971	81,122
PROVISION FOR INCOME TAXES	11,943	12,277	10,841	9,194	3,308	6,642	6,615	6,184	5,831	7,284	8,696	5,241	44,255	22,749	27,052
NET INCOME	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 11,713	$ 14,821	$ 16,987	$ 10,549	85,385	45,222	54,070
Banner Corporation
INTEREST INCOME:
Interest-bearing deposits													127	122	96
OTHER INCOME (EXPENSE):
Dividend income from subsidiaries													50,971	170,260	26,027
Equity in undistributed (distributions in excess of) income of subsidiaries													40,852	(116,120)	33,612
Other income													60	69	67
Net change in valuation of financial instruments carried at fair value													(2,720)	(2,714)	(4,073)
Interest on other borrowings													(4,040)	(3,247)	(2,914)
Other expenses													(3,450)	(7,175)	(2,519)
Income before provision for income taxes													81,800	41,195	50,296
PROVISION FOR INCOME TAXES													(3,585)	(4,027)	(3,774)
NET INCOME													$ 85,385	$ 45,222	$ 54,070