SHORT-TERM BORROWINGS AND LONG-TERM DEBT - Narrative (Details)		1 Months Ended		9 Months Ended	12 Months Ended
	Oct. 20, 2020 USD ($)	Dec. 31, 2004 USD ($)	Sep. 30, 2004 USD ($)	Sep. 30, 2023 USD ($) period	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)
Debt Instrument [Line Items]
Short-term borrowings				$ 0	$ 5,000,000
Long term borrowings				156,041,000	105,859,000
Investment securities				1,265,306,000	1,336,677,000
Unamortized debt issuance costs				$ (506,000)	(688,000)
Subordinated Debt
Debt Instrument [Line Items]
Number of periods interest can be deferred | period				20
C P B Capital Trust I V
Debt Instrument [Line Items]
Trust preferred securities issued value			$ 30,000,000
Common securities issued			$ 900,000
C P B Capital Trust I V | Subordinated Debt
Debt Instrument [Line Items]
Long term borrowings				$ 30,900,000
C P B Capital Trust V
Debt Instrument [Line Items]
Trust preferred securities issued value		$ 20,000,000
Common securities issued		$ 600,000
C P B Capital Trust V | Subordinated Debt
Debt Instrument [Line Items]
Long term borrowings				$ 20,600,000
Maximum | Subordinated Debt
Debt Instrument [Line Items]
Redemption period				90 days
Federal Home Loan Bank Borrowings
Debt Instrument [Line Items]
Line of Credit, maximum borrowing capacity				$ 1,940,000,000	2,230,000,000
Unused borrowings available				1,820,000,000	2,190,000,000
Short-term borrowings				0	5,000,000
Letters of Credit, outstanding				72,000,000	36,000,000
Long term borrowings				50,000,000	0
Federal Home Loan Bank Borrowings | Asset Pledged as Collateral
Debt Instrument [Line Items]
Net loans and leases				$ 3,190,000,000
Federal Home Loan Bank Borrowings | Minimum
Debt Instrument [Line Items]
Long term borrowings, interest rate				4.02%
Federal Home Loan Bank Borrowings | Maximum
Debt Instrument [Line Items]
Long term borrowings, interest rate				4.62%
Federal Reserve discount window line of credit
Debt Instrument [Line Items]
Unused borrowings available				$ 290,300,000	75,900,000
Federal Reserve discount window line of credit | Asset Pledged as Collateral
Debt Instrument [Line Items]
Net loans and leases				136,700,000	125,000,000
Investment securities				199,700,000	$ 0
Notes | Subordinated notes
Debt Instrument [Line Items]
Long term borrowings				$ 54,500,000
Debt face amount	$ 55,000,000
Debt instrument, term	10 years
Stated interest rate, first five years	4.75%			0.0475%	0.0475%
Unamortized debt issuance costs				$ (500,000)
Notes | Subordinated notes | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate	4.56%
Pacific Coast Bankers' Bank ("PCBB")
Debt Instrument [Line Items]
Line of Credit, maximum borrowing capacity					$ 100,000,000	$ 50,000,000
Wells Fargo
Debt Instrument [Line Items]
Line of Credit, maximum borrowing capacity						$ 25,000,000
Trust IV | Junior Subordinated Debt | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.26%
Trust IV | Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) 1
Debt Instrument [Line Items]
Basis spread on variable rate			2.45%		2.45%
Trust V | Junior Subordinated Debt | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.26%
Trust V | Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) 1
Debt Instrument [Line Items]
Basis spread on variable rate		1.87%			1.87%