BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Textuals) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) subsidiary office location	Dec. 31, 2018 USD ($)
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	175
Number of production offices | office	18
Subsidiary, Islanders Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of locations | location	3,000
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
Not Designated as Hedging Instrument [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount	$ 493,607	$ 310,931
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount	371,957	272,374
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount	$ 3,567	$ 3,973