BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
INTEREST INCOME:
Certificates, time deposits and dividends	$ 41,534	$ 42,698	$ 42,290	$ 41,126	$ 41,586	$ 41,728	$ 41,201	$ 40,056	$ 40,757	$ 39,922	$ 38,941	$ 38,150	$ 167,648	$ 164,571	$ 157,770
OTHER INCOME (EXPENSE):
Other income													4,697	2,506	2,302
Other expenses													(12,795)	(12,135)	(11,856)
Income (loss) before provision for (benefit from) income taxes	19,326	18,027	(6,440)	9,184	5,070	6,030	2,199	(7,842)	(12,691)	(18,754)	(8,897)	(3,541)	40,097	5,457	(43,883)
PROVISION FOR (BENEFIT FROM) INCOME TAXES	4,638	2,407	(31,830)	0	0	0	0	0	0	23,988	(3,951)	(2,024)	(24,785)	0	18,013
NET INCOME (LOSS)	14,688	15,620	25,390	9,184	5,070	6,030	2,199	(7,842)	(12,691)	(42,742)	(4,946)	(1,517)	64,882	5,457	(61,896)
Banner Corporation
INTEREST INCOME:
Certificates, time deposits and dividends													218	277	362
OTHER INCOME (EXPENSE):
Dividend income from subsidiaries													61,329	990	1,760
Equity in undistributed income of subsidiaries													23,507	9,478	(58,766)
Other income													55	46	46
Net change in valuation of financial instruments carried at fair value													(23,075)	(1,563)	(730)
Interest on other borrowings													(3,395)	(4,193)	(4,226)
Other expenses													(2,375)	(2,313)	(2,818)
Income (loss) before provision for (benefit from) income taxes													56,264	2,722	(64,372)
PROVISION FOR (BENEFIT FROM) INCOME TAXES													(8,618)	(2,735)	(2,476)
NET INCOME (LOSS)													$ 64,882	$ 5,457	$ (61,896)