Document and Entity Information Document - shares	9 Months Ended
	Sep. 30, 2017	Nov. 03, 2017
Entity Information [Line Items]
Entity Registrant Name	Banner Corporation
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Entity Central Index Key	0000946673
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Voting Common Stock [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		32,806,473
Nonvoting Common Stock [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		100,029