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.

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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

+ Details

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

- Definition

Indicates the number of mortgages under each classification.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.3)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

+ Details

Name:	us-gaap_MortgageLoansOnRealEstateNumberOfLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=banc_NontraditionalMortgageLoansPortfolioMember
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_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_FirstMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=banc_GreenLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=banc_InterestOnlyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=banc_NegativeAmortizationLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_SecondMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LOANS AND LEASES AND ALLOWANCE FOR LOAN AND LEASE LOSSES - Non Traditional Mortgages Portfolio (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($) Loan	Mar. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,930,507	$ 6,659,407	$ 6,105,321
NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 846,800	$ 806,933
Consumer \| NTM Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	621	592
Loans	$ 846,800	$ 806,933
Consumer \| NTM Loans \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	100.00%	100.00%
Consumer \| NTM Loans \| Loan Portfolio Concentration Risk \| Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	12.20%	12.10%
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	609	580
Loans	$ 843,255	$ 803,355
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	99.60%	99.60%
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	99	101
Loans	$ 79,248	$ 82,197
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Green Loans \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	9.40%	10.20%
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Interest Only Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	499	468
Loans	$ 760,370	$ 717,484
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Interest Only Loans \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	89.80%	88.90%
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Negative amortization
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	11	11
Loans	$ 3,637	$ 3,674
Consumer \| NTM Loans \| Green Loans (HELOC) - first liens \| Negative amortization \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.40%	0.50%
Consumer \| NTM Loans \| Green Loans (HELOC) - second liens
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	12	12
Loans	$ 3,545	$ 3,578
Consumer \| NTM Loans \| Green Loans (HELOC) - second liens \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.40%	0.40%
Consumer \| NTM Loans \| Green Loans (HELOC) - second liens \| Green Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Count \| Loan	12	12
Loans	$ 3,545	$ 3,578
Consumer \| NTM Loans \| Green Loans (HELOC) - second liens \| Green Loans \| Loan Portfolio Concentration Risk \| Nontraditional Mortgage Loans Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk percentage	0.40%	0.40%