BUSINESS COMBINATION - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Nov. 01, 2019	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill		$ 373,121	$ 373,121	$ 339,154
AltaPacific Bank [Member]
Business Acquisition [Line Items]
Business Combination, Acquired Receivables, Gross Contractual Amount	$ 338,200
Business Acquisition, Effective Date of Acquisition	Nov. 01, 2019
Cash paid	$ 2,360
Fair value of common shares issued	85,200
Total consideration	87,560
Cash and cash equivalents	39,686
Securities	20,348
business combination, recognized identifiable assets acquired and liabilities assumed, federal home loan bank stock	2,005
Loans receivable (contractual amount of $338.2 million)	332,355
Real estate owned held for sale	650
Property and equipment	3,809
Core deposit intangible	4,610
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Bank Owned Life Insurance	11,890
Deferred tax asset	166
Other assets	10,150
Total assets acquired	425,669
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
Other liabilities	8,154
Total liabilities assumed	372,076
Net assets acquired	53,593
Goodwill	$ 33,967