REGULATORY CAPITAL REQUIREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Total capital to risk-weighted assets:
Actual	$ 684,583	$ 631,674
Actual, Ratio	16.80%	16.99%
Minimum for Capital Adequacy Purposes	326,071	297,493
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%
Tier 1 capital to risk-weighted assets:
Actual	633,317	584,838
Actual, Ratio	15.54%	15.73%
Minimum for Capital Adequacy Purposes	163,036	148,747
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	6.00%
Tier 1 leverage capital to average assets:
Actual	633,317	584,838
Actual, Ratio	13.41%	13.64%
Minimum for Capital Adequacy Purposes	188,885	171,553
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%
Banner Bank [Member]
Total capital to risk-weighted assets:
Actual	605,997	557,253
Actual, Ratio	15.53%	15.75%
Minimum for Capital Adequacy Purposes	312,220	282,984
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	390,274	353,730
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual	556,897	512,689
Actual, Ratio	14.27%	14.49%
Minimum for Capital Adequacy Purposes	156,110	141,192
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	234,165	212,238
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	6.00%	6.00%
Tier 1 leverage capital to average assets:
Actual	556,897	512,689
Actual, Ratio	12.42%	12.65%
Minimum for Capital Adequacy Purposes	179,304	162,174
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	224,130	202,707
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%
Islanders Bank
Total capital to risk-weighted assets:
Actual	36,590	34,795
Actual, Ratio	19.92%	18.73%
Minimum for Capital Adequacy Purposes	14,693	14,859
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	18,367	18,574
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual	34,332	32,469
Actual, Ratio	18.69%	17.48%
Minimum for Capital Adequacy Purposes	7,347	7,430
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	11,020	11,144
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	6.00%	6.00%
Tier 1 leverage capital to average assets:
Actual	34,332	32,469
Actual, Ratio	13.68%	13.60%
Minimum for Capital Adequacy Purposes	10,040	9,553
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 12,550	$ 11,941
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%