JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) subsidiary	Dec. 31, 2017 USD ($)
Schedule of Trust Preferred Securities [Line Items]
Number of wholly-owned Grantor Trusts | subsidiary	9
Grantor trusts amount of tier one risk based capital	$ 1,203,155	$ 1,123,154
Debentures Subject to Mandatory Redemption [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	140,212
Fair value adjustment	(26,121)
Total TPS liability at fair value	$ 114,091
Current Interest Rate	4.71%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trusts [Member]
Schedule of Trust Preferred Securities [Line Items]
Grantor trusts amount of tier one risk based capital	$ 136,000
Grantor trusts percentage of tier one risk based capital	10.40%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,464
Current Interest Rate	5.79%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	3.35%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,465
Current Interest Rate	5.34%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.90%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,465
Current Interest Rate	5.29%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.85%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	4.22%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.57%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	4.36%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.62%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	3.78%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.38%
Debentures Subject to Mandatory Redemption [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 8,248
Current Interest Rate	5.49%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.70%
Debentures Subject to Mandatory Redemption [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 4,124
Current Interest Rate	5.79%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	3.35%
Debentures Subject to Mandatory Redemption [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 4,124
Current Interest Rate	4.47%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.68%
Aggregate Liquidation Amount of Trust Preferred Securities [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 136,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	8,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,000
Aggregate Liquidation Amount of Common Capital Securities [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,212
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	464
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	465
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	465
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	248
Aggregate Liquidation Amount of Common Capital Securities [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	124
Aggregate Liquidation Amount of Common Capital Securities [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 124