BUSINESS COMBINATION AND BRANCH DIVESTITURE (Details) $ in Thousands	Nov. 01, 2019 USD ($) shares	Nov. 01, 2018 USD ($) bank_branch shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield			$ 4,518	$ 5,216	$ 6,520
Goodwill			$ 373,121	$ 339,154	$ 242,659	$ 244,583
AltaPacific Bank [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 2,360
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2019
Business Combination, Ratio of Shares Acquired to Shares Exchanged | shares	0.2712
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition	$ 4,835
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield	(683)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value	4,152
Business Combination, Consideration Transfered, Equity Interests Issued and Issuable, Shares	85,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	425,669
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	313,374
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Advances From FHLB	40,226
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Junior Subordinated Debentures	5,814
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Compensation	4,508
Business Combination, Acquired Receivable, Fair Value	332,355
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	4,610
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Bank Owned Life Insurance	11,890
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets	166
Goodwill	33,967
Business Combination, Acquired Receivables, Non-Credit-Impaired	333,500
Business Combination, consideration transfered	87,560
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	39,686
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	20,348
business combination, recognized identifiable assets acquired and liabilities assumed, federal home loan bank stock	2,005
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Real Estate Held for Sale	650
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	3,809
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liability, Other	8,154
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	372,076
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	53,593
Business Combination, Acquired Receivables, Non-Credit-Impaired, Fair Value	328,200
Business Combination, Acquired Receivables, Non-Credit-Impaired, Discount	5,300
Business Combination, Acquired Receivables, Non-Credit-Impaired, Credit Related Discount	5,800
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition	5,881
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Non-Accretable Difference	$ (1,046)
Business combination, CDI acquired useful life	10 years
Skagit Bank [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 329
Business Acquisition, Effective Date of Acquisition		Nov. 01, 2018
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition		$ 7,982
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield		(995)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value		$ 6,987
Business combination, number of branches | bank_branch		11
Business Combination, Consideration Transfered, Equity Interests Issued and Issuable, Shares | shares		3,100,000
Business Combination, Consideration Transfered, Equity Interests Issued and Issuable, Shares		$ 179,709
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		915,821
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits		810,209
Business Combination, Acquired Receivable, Fair Value		632,374
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		16,368
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets		95
Goodwill		96,495
Business Combination, Acquired Receivables, Non-Credit-Impaired		637,400
Business Combination, consideration transfered		180,038
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		19,167
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities		210,326
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Real Estate Held for Sale		2,593
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		15,788
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	$ 10,150	19,110
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liability, Other		22,069
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		832,278
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		83,543
Business Combination, Acquired Receivables, Non-Credit-Impaired, Fair Value		625,200
Business Combination, Acquired Receivables, Non-Credit-Impaired, Discount		12,200
Business Combination, Acquired Receivables, Non-Credit-Impaired, Credit Related Discount		7,900
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition		9,897
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Non-Accretable Difference		$ (1,915)
Business combination, CDI acquired useful life		9 years