STOCK-BASED COMPENSATION PLANS AND STOCK OPTIONS (Details) (USD $)			3 Months Ended		9 Months Ended		0 Months Ended	9 Months Ended	15 Months Ended	0 Months Ended	34 Months Ended		34 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Apr. 24, 2012 2012 Restricted Stock Plan [Member] Restricted Stock [Member] increment	Sep. 30, 2013 2012 Restricted Stock Plan [Member] Restricted Stock [Member]	Jun. 30, 2013 2012 Restricted Stock Plan [Member] Restricted Stock [Member]	Aug. 23, 2010 CEO Employment Agreement Restricted Stock Plan [Member] Restricted Stock [Member]	Jun. 30, 2013 CEO Employment Agreement Restricted Stock Plan [Member] Restricted Stock [Member]	Sep. 30, 2013 CEO Employment Agreement Restricted Stock Plan [Member] Restricted Stock [Member]	Jun. 30, 2013 CEO Employment Agreement Restricted Stock Plan [Member] Restricted Stock [Member] Chief Executive Officer [Member]	Sep. 30, 2013 SOPs [Member] Stock Options [Member]	Sep. 30, 2012 SOPs [Member] Stock Options [Member]	Sep. 30, 2013 SOPs [Member] Stock Options [Member]	Sep. 30, 2012 SOPs [Member] Stock Options [Member]	Sep. 30, 2013 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, 2013 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]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Increments Shares Vest Annually							3
Award Vesting Period							3 years			3 years
Share-based Compensation Expense			$ 482,000	$ 193,000	$ 1,004,000	$ 293,000								$ 0	$ 0	$ 0	$ 6,000	$ 286,000	$ 105,000	$ 526,000	$ 181,000
Compensation Cost Not yet Recognized			3,700,000		3,700,000
Compensation Cost Not yet Recognized, Period for Recognition								31 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
Restricted stock granted								189,426					34,257
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period									31,178		28,359
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number								158,248				5,898
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	0	0
Deferred Compensation Liability	$ 15,642,000	$ 14,452,000																$ 1,079,000		$ 1,079,000