REGULATORY CAPITAL REQUIREMENTS (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Total capital to risk-weighted assets:
Actual	$ 1,663,943	$ 1,608,387
Actual, Ratio	0.1471	0.1473
Minimum for Capital Adequacy Purposes	$ 904,633	$ 873,472
Minimum for Capital Adequacy Purposes, Ratio	0.0800	0.0800
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 1,130,791	$ 1,091,840
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.1000	0.1000
Tier 1 capital to risk-weighted assets:
Actual	$ 1,440,694	$ 1,371,736
Actual, Ratio	0.1274	0.1256
Minimum for Capital Adequacy Purposes	$ 678,474	$ 655,104
Minimum for Capital Adequacy Purposes, Ratio	0.0600	0.0600
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 678,474	$ 655,104
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0600	0.0600
Tier 1 leverage capital to average assets:
Actual	$ 1,440,694	$ 1,371,736
Actual, Ratio	0.0876	0.0950
Minimum for Capital Adequacy Purposes	$ 658,091	$ 577,331
Minimum for Capital Adequacy Purposes, Ratio	0.0400	0.0400
Tier 1 common equity to risk-weighted assets:
Banking Regulation, Common Equity Tier One Risk-Based Capital, Actual	$ 1,305,194	$ 1,228,236
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Actual	0.1154	0.1125
Banking Regulation, Common Equity Tier One Risk-Based Capital, Capital Adequacy, Minimum	$ 508,856	$ 491,328
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Capital Adequacy, Minimum	0.0450	0.0450
Banner Bank [Member]
Total capital to risk-weighted assets:
Actual	$ 1,552,204	$ 1,438,012
Actual, Ratio	0.1373	0.1339
Minimum for Capital Adequacy Purposes	$ 904,159	$ 859,260
Minimum for Capital Adequacy Purposes, Ratio	0.0800	0.0800
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 1,130,199	$ 1,074,075
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.1000	0.1000
Tier 1 capital to risk-weighted assets:
Actual	$ 1,428,955	$ 1,303,590
Actual, Ratio	0.1264	0.1214
Minimum for Capital Adequacy Purposes	$ 678,119	$ 644,445
Minimum for Capital Adequacy Purposes, Ratio	0.0600	0.0600
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 904,159	$ 859,260
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0800	0.0800
Tier 1 leverage capital to average assets:
Actual	$ 1,428,955	$ 1,303,590
Actual, Ratio	0.0869	0.0922
Minimum for Capital Adequacy Purposes	$ 657,882	$ 565,620
Minimum for Capital Adequacy Purposes, Ratio	0.0400	0.0400
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 822,353	$ 707,025
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0500	0.0500
Tier 1 common equity to risk-weighted assets:
Banking Regulation, Common Equity Tier One Risk-Based Capital, Actual	$ 1,428,955	$ 1,303,590
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Actual	0.1264	0.1214
Banking Regulation, Common Equity Tier One Risk-Based Capital, Capital Adequacy, Minimum	$ 508,589	$ 483,334
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Capital Adequacy, Minimum	0.0450	0.0450
Banking Regulation, Common Equity Tier One Risk-Based Capital, Well Capitalized, Minimum	$ 734,629	$ 698,149
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Well Capitalized, Minimum	0.0650	0.0650
Islanders Bank
Total capital to risk-weighted assets:
Actual		$ 29,333
Actual, Ratio		0.1565
Minimum for Capital Adequacy Purposes		$ 14,997
Minimum for Capital Adequacy Purposes, Ratio		0.0800
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions		$ 18,747
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio		0.1000
Tier 1 capital to risk-weighted assets:
Actual		$ 26,983
Actual, Ratio		0.1439
Minimum for Capital Adequacy Purposes		$ 11,248
Minimum for Capital Adequacy Purposes, Ratio		0.0600
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions		$ 14,997
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio		0.0800
Tier 1 leverage capital to average assets:
Actual		$ 26,983
Actual, Ratio		0.0787
Minimum for Capital Adequacy Purposes		$ 13,720
Minimum for Capital Adequacy Purposes, Ratio		0.0400
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions		$ 17,150
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio		0.0500
Tier 1 common equity to risk-weighted assets:
Banking Regulation, Common Equity Tier One Risk-Based Capital, Actual		$ 26,983
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Actual		0.1439
Banking Regulation, Common Equity Tier One Risk-Based Capital, Capital Adequacy, Minimum		$ 8,436
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Capital Adequacy, Minimum		0.0450
Banking Regulation, Common Equity Tier One Risk-Based Capital, Well Capitalized, Minimum		$ 12,185
Banking Regulation, Common Equity Tier One Risk-Based Capital Ratio, Well Capitalized, Minimum		0.0650