Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

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

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract
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

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_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
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

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

FAIR VALUE MEASUREMENTS - Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Available for sale debt securities, at fair value	$ 623,499		$ 625,074
Equity securities	12,070		11,782
Mortgage servicing rights	1,850	$ 2,028	2,657	$ 2,966	$ 3,172	$ 3,463
Financial liabilities:
Impaired loans	886		2,509
With no related allowance recorded	5,217		5,129
Residential MBS
Financial assets:
Available for sale debt securities, at fair value	235,840		145,192
Commercial MBS and CMOs
Financial assets:
Available for sale debt securities, at fair value	372,279		356,169
Agency bonds
Financial assets:
Available for sale debt securities, at fair value	15,380		123,713
Fair Value
Financial assets:
Available for sale debt securities, at fair value	623,499		625,074
Equity securities	12,070		11,782
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	10,834		746
Fair Value \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Level 2
Financial assets:
Available for sale debt securities, at fair value	623,499		625,074
Equity securities	12,070		11,782
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	10,834		746
Fair Value \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis
Financial assets:
Available for sale debt securities, at fair value	623,499		625,074
Equity securities	12,070		11,782
Mortgage servicing rights	1,850		2,657
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	10,834		746
Fair Value \| Recurring Basis \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Mortgage servicing rights	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis \| Level 2
Financial assets:
Available for sale debt securities, at fair value	623,499		625,074
Equity securities	12,070		11,782
Mortgage servicing rights	0		0
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	10,834		746
Fair Value \| Recurring Basis \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Mortgage servicing rights	1,850		2,657
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis \| Residential MBS
Financial assets:
Available for sale debt securities, at fair value	235,840		145,192
Fair Value \| Recurring Basis \| Residential MBS \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Residential MBS \| Level 2
Financial assets:
Available for sale debt securities, at fair value	235,840		145,192
Fair Value \| Recurring Basis \| Residential MBS \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Commercial MBS and CMOs
Financial assets:
Available for sale debt securities, at fair value	372,279		356,169
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 2
Financial assets:
Available for sale debt securities, at fair value	372,279		356,169
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Agency bonds
Financial assets:
Available for sale debt securities, at fair value	15,380		123,713
Fair Value \| Recurring Basis \| Agency bonds \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Agency bonds \| Level 2
Financial assets:
Available for sale debt securities, at fair value	15,380		123,713
Fair Value \| Recurring Basis \| Agency bonds \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Single family residential
Financial liabilities:
Impaired loans	886		2,509
With no related allowance recorded	4,689		4,588
Single family residential \| Permanent mortgages
Financial liabilities:
Impaired loans			1,600
With no related allowance recorded	1,600
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 1
Financial liabilities:
Impaired loans			0
With no related allowance recorded	0
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 2
Financial liabilities:
Impaired loans			0
With no related allowance recorded	0
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 3
Financial liabilities:
Impaired loans			790
With no related allowance recorded	858
Single family residential \| Permanent mortgages \| Fair Value \| Nonrecurring Basis
Financial liabilities:
Impaired loans			$ 790
With no related allowance recorded	$ 858