BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES:
Net income	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 11,713	$ 14,821	$ 16,987	$ 10,549	$ 85,385	$ 45,222	$ 54,070
Adjustments to reconcile net income to net cash provided from operating activities:
Decrease in deferred taxes													7,883	(3,906)	2,966
Net change in valuation of financial instruments carried at fair value													2,620	813	(1,374)
Decrease (increase) in other assets													3,759	(7,319)	(2,310)
Increase in other liabilities													(6,664)	4,090	3,370
Net cash (used by) provided from operating activities													(76,688)	15,369	98,066
INVESTING ACTIVITIES:
Net cash provided from (used by) investing activities													146,447	15,059	(164,067)
FINANCING ACTIVITIES:
Issuance of stock for shareholder reinvestment program													0	34	127
Cash dividends paid													(28,282)	(17,170)	(13,462)
Net cash (used by) provided from financing activities													(83,957)	105,417	54,724
NET CHANGE IN CASH AND CASH EQUIVALENTS													(14,198)	135,845	(11,277)
CASH AND DUE FROM BANKS, BEGINNING OF YEAR				117,657									117,657
CASH AND DUE FROM BANKS, END OF YEAR	177,083				117,657								177,083	117,657
Banner Corporation
OPERATING ACTIVITIES:
Net income													85,385	45,222	54,070
Adjustments to reconcile net income to net cash provided from operating activities:
Distributions in excess of (equity in undistributed) income of subsidiaries													(40,852)	116,120	(33,612)
Decrease in deferred taxes													(702)	(1,398)	(1,444)
Net change in valuation of financial instruments carried at fair value													2,720	2,714	4,073
Decrease (increase) in other assets													7,332	(10,655)	(3,822)
Increase in other liabilities													3,233	3,919	222
Net cash (used by) provided from operating activities													57,116	155,922	19,487
INVESTING ACTIVITIES:
Funds transferred to deferred compensation trust													(26)	(26)	(26)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries													50,000	0	0
Acquisitions													0	132,652	0
Net cash provided from (used by) investing activities													49,974	(132,678)	(26)
FINANCING ACTIVITIES:
Issuance of stock for shareholder reinvestment program													0	34	127
Payments for Repurchase of Preferred Stock and Preference Stock													50,772	0	0
Cash dividends paid													(28,282)	(17,170)	(13,462)
Net cash (used by) provided from financing activities													(79,054)	(17,136)	(13,335)
NET CHANGE IN CASH AND CASH EQUIVALENTS													28,036	6,108	6,126
CASH AND DUE FROM BANKS, BEGINNING OF YEAR				$ 58,232				$ 52,124				$ 45,998	58,232	52,124	45,998
CASH AND DUE FROM BANKS, END OF YEAR	$ 86,268				$ 58,232				$ 52,124				$ 86,268	$ 58,232	$ 52,124