STOCK-BASED COMPENSATION PLANS AND STOCK OPTIONS (Details) (USD $)			3 Months Ended		9 Months Ended		0 Months Ended		9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Restricted Stock [Member] Chief Executive Officer [Member]	Sep. 30, 2011 Restricted Stock [Member] Chief Executive Officer [Member]	Sep. 30, 2012 Restricted Stock [Member] Chief Executive Officer [Member]	Sep. 30, 2011 Restricted Stock [Member] Chief Executive Officer [Member]	Apr. 24, 2012 2012 Restricted Stock Plan [Member] Restricted Stock [Member] increment	Apr. 24, 2012 2012 Restricted Stock Plan [Member] Restricted Stock [Member] Chief Executive Officer [Member]	Sep. 30, 2012 2012 Restricted Stock Plan [Member] Restricted Stock [Member] Officer [Member]	Sep. 30, 2012 SOPs [Member] Stock Options [Member]	Sep. 30, 2011 SOPs [Member] Stock Options [Member]	Sep. 30, 2012 SOPs [Member] Stock Options [Member]	Sep. 30, 2011 SOPs [Member] Stock Options [Member]	Sep. 30, 2012 Banner Corporation Long-Term Incentive Plan [Member] Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2011 Banner Corporation Long-Term Incentive Plan [Member] Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2012 Banner Corporation Long-Term Incentive Plan [Member] Stock Appreciation Rights (SARs) [Member]	Sep. 30, 2011 Banner Corporation Long-Term Incentive Plan [Member] Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Increments Shares Vest Annually							3
Award Vesting Period							3 years
Share-based Compensation Expense			$ 193,000	$ 28,000	$ 293,000	$ 69,000				$ 0	$ 3,000	$ 6,000	$ 22,000		$ 28,000	$ 181,000	$ 60,000
Compensation Cost Not yet Recognized			2,100,000		2,100,000
Compensation Cost Not yet Recognized, Period for Recognition					36 months
Number of Shares Authorized							300,000			2,284,186		2,284,186
Share-based Compensation, Shares Authorized Under Stock Option Plans, Exercise Price Percentage of Fair Value of Stock												100.00%
Maximum Contractual Term							10 years
Stock Issued During Period, Value								300,000
Stock Issued During Period, Shares								14,535
Stock Grants in Period									77,500
Annual Vesting Percentage												20.00%
Award Termination												10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Forfeiture												90 days
Options, Grants in Period										0	0	0	0
Oprtions, Exercises in Period										0		0
Number of Business Days Following Public Annoucement, Board is Authorized to Reprice Certain Awards																3 days
Tax Benefit from Compensation Expense														105,000
Deferred Compensation Liability	$ 14,375,000	$ 13,306,000												$ 465,000		$ 465,000