LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loans Individually Evaluated for Impairment by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Unpaid Principal Balance
Total	$ 76,097		$ 76,097		$ 49,814
Recorded Investment
Total	75,225		75,225		49,708
Allowance for Loan and Lease Losses	12,575		12,575		5,990
Average Recorded Investment	75,814	$ 48,879	68,508	$ 40,519
Interest Income Recognized	75	321	156	386
Cash Basis Interest Recognized	56	309	128	365
Commercial \| Commercial and industrial
Unpaid Principal Balance
With no related allowance recorded	11,455		11,455		1,471
With an allowance recorded	19,739		19,739		18,776
Recorded Investment
With no related allowance recorded	11,383		11,383		1,460
With an allowance recorded	19,746		19,746		18,776
Allowance for Loan and Lease Losses	9,697		9,697		3,367
Average Recorded Investment	29,992	20,794	26,452	12,921
Interest Income Recognized	16	255	37	255
Cash Basis Interest Recognized	18	254	39	254
Commercial \| Commercial real estate
Unpaid Principal Balance
With no related allowance recorded	5,418		5,418		0
Recorded Investment
With no related allowance recorded	5,168		5,168		0
Average Recorded Investment	5,210	0	3,992	289
Interest Income Recognized	0	0	0	0
Cash Basis Interest Recognized	0	0	0	0
Commercial \| SBA
Unpaid Principal Balance
With no related allowance recorded	1,474		1,474		1,439
With an allowance recorded	3,731		3,731		3,921
Recorded Investment
With no related allowance recorded	1,417		1,417		1,379
With an allowance recorded	3,542		3,542		3,757
Allowance for Loan and Lease Losses	2,878		2,878		2,045
Average Recorded Investment	5,172	3,297	5,293	3,571
Interest Income Recognized	3	4	6	8
Cash Basis Interest Recognized	4	4	7	8
Commercial \| Construction
Recorded Investment
Average Recorded Investment		2,519		2,519
Interest Income Recognized		0		0
Cash Basis Interest Recognized		0		0
Consumer \| Single family residential mortgage
Unpaid Principal Balance
With no related allowance recorded	32,849		32,849		19,319
With an allowance recorded	0		0		4,213
Recorded Investment
With no related allowance recorded	32,999		32,999		19,405
With an allowance recorded	0		0		4,252
Allowance for Loan and Lease Losses	0		0		574
Average Recorded Investment	33,356	21,092	31,420	20,208
Interest Income Recognized	56	58	110	116
Cash Basis Interest Recognized	34	48	79	97
Consumer \| Other consumer
Unpaid Principal Balance
With no related allowance recorded	1,431		1,431		671
With an allowance recorded	0		0		4
Recorded Investment
With no related allowance recorded	970		970		675
With an allowance recorded	0		0		4
Allowance for Loan and Lease Losses	0		0		$ 4
Average Recorded Investment	2,084	1,177	1,351	1,011
Interest Income Recognized	0	4	3	7
Cash Basis Interest Recognized	$ 0	$ 3	$ 3	$ 6

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banc_CommercialandIndustrialReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banc_CommercialSmallBusinessAdministrationReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banc_ConsumerSingleFamilyResidentialMortgageReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banc_OtherConsumerLoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: