LOANS AND CREDIT QUALITY - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) portfolioSegment	Dec. 31, 2022 USD ($)
Financing Receivable, Impaired [Line Items]
Number of portfolio segments | portfolioSegment	2
Allowance for unfunded commitments	$ 1,800	$ 2,200
Accrued interest receivable	28,900	26,900
Loans held for investment ("LHFI")	$ 7,382,404	$ 7,384,820
Washington | Residential Mortgage and Multifamily
Financing Receivable, Impaired [Line Items]
Percentage of loan portfolio	11.00%
California | Multifamily
Financing Receivable, Impaired [Line Items]
Percentage of loan portfolio		36.00%
Federal Home Loan Bank Advances | Asset Pledged as Collateral without Right
Financing Receivable, Impaired [Line Items]
Loans held for investment ("LHFI")	$ 5,100,000	$ 5,200,000
Federal Reserve Bank Advances | Asset Pledged as Collateral without Right
Financing Receivable, Impaired [Line Items]
Loans held for investment ("LHFI")	$ 1,200,000	$ 497,000