Document and Entity Information Document - shares	6 Months Ended
	Jun. 30, 2021	Jul. 31, 2021
Document and Entity Information [Abstract]
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	BANR
Security Exchange Name	NASDAQ
Entity Registrant Name	BANNER CORPORATION
Entity Incorporation, State or Country Code	WA
Entity Tax Identification Number	91-1691604
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	000-26584
Amendment Flag	false
Entity Central Index Key	0000946673
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		34,551,718
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Address, Address Line One	10 South First Avenue
Entity Address, City or Town	Walla Walla
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	99362
City Area Code	509
Local Phone Number	527-3636