BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Textuals) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) subsidiary office location
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of wholly-owned subsidiaries | subsidiary	2
Subsidiary, Banner Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of offices | office	179
Number of production offices | office	17
Subsidiary, Islanders Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of locations | location	3
Minimum [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	3 years
Minimum [Member] | Core Deposit Intangibles [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	3 years
Maximum [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	10 years
Maximum [Member] | Core Deposit Intangibles [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	10 years
Loans Receivable [Member] | Interest Rate Swap [Member] | F&M Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount | $	$ 4.0
Other assets [Member] | Interest Rate Swap [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount | $	$ 272.4