BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Other assets	$ 168,632	$ 74,108
Total assets	12,604,031	11,871,317
LIABILITIES AND SHAREHOLDERS’ EQUITY
Junior subordinated debentures at fair value	119,304	114,091
Shareholders’ equity	1,594,034	1,478,595	$ 1,272,626	$ 1,305,710
Total liabilities and stockholders' equity	12,604,031	11,871,317
Banner Corporation
ASSETS
Cash	54,257	38,029
Investment in trust equities	4,444	4,212
Investment in subsidiaries	1,691,907	1,540,251
Other assets	19,471	25,267
Total assets	1,770,079	1,607,759
LIABILITIES AND SHAREHOLDERS’ EQUITY
Miscellaneous liabilities	52,322	15,073
Deferred tax liability	4,419	0
Junior subordinated debentures at fair value	119,304	114,091
Shareholders’ equity	1,594,034	1,478,595
Total liabilities and stockholders' equity	$ 1,770,079	$ 1,607,759