LOANS AND ALLOWANCE FOR CREDIT LOSSES - Non Traditional Mortgage Loans Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 6,961,032	$ 7,115,038
NTM Loans \| Loan Portfolio \| Loan Portfolio Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage to total loans and leases (percent)	11.40%	12.10%
NTM Loans \| Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 792,000	$ 862,300
Decrease in Non-Traditional Mortgage portfolio loans	70,400
NTM Loans \| Consumer \| Non-performing Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 15,300	$ 3,000
Weighted average LTV (percent)	60.00%
NTM Loans \| Consumer \| Interest Only \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loan term (in years)	40 years
Mortgage loan, flexible initial term (in years)	10 years
NTM Loans \| Consumer \| Interest Only \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loan, flexible initial term (in years)	1 year
NTM Loans \| Consumer \| Loan Portfolio \| Loan Portfolio Concentration Risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in Non-Traditional Mortgage portfolio loans (percent)	8.20%

Financing Receivable, Excluding Accrued Interest, Increase (Decrease)

No definition available.

Name:	banc_FinancingReceivableExcludingAccruedInterestIncreaseDecrease
Namespace Prefix:	banc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable, Excluding Accrued Interest, Increase (Decrease), Percentage

+ References

No definition available.

+ Details

Name:	banc_FinancingReceivableExcludingAccruedInterestIncreaseDecreasePercentage
Namespace Prefix:	banc_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Mortgage Loan, Flexible Initial Term

+ References

No definition available.

+ Details

Name:	banc_FinancingReceivableMortgageLoanFlexibleInitialTerm
Namespace Prefix:	banc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Mortgage Loan, Term

+ References

No definition available.

+ Details

Name:	banc_FinancingReceivableMortgageLoanTerm
Namespace Prefix:	banc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Non-Traditional Mortgage Performance Indicators, Weighted Average Loan To Value ratio, Percentage

+ References

No definition available.

+ Details

Name:	banc_NonTraditionalMortgagePerformanceIndicatorsWeightedAverageLoanToValueRatioPercentage
Namespace Prefix:	banc_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482861/275-10-50-18

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482861/275-10-50-20

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-5

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=banc_LoansAndFinanceReceivablesNonTraditionalMortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=banc_LoanPortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=banc_LoanPortfolioConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=banc_InterestOnlyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: