Fair Value Measurement and Fair Value of Financial Instruments- Carrying Values and Fair Values of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial Assets:
Carrying Value	$ 847,699	$ 923,308
Fair Value	656,725	760,455
Federal Home Loan Bank and other membership bank stocks, Carrying Value	53,580	42,483
Federal Home Loan Bank and other membership bank stocks, Fair Value	53,580	42,483
Loans	8,218,898	7,795,786
Fair Value	7,722,899	7,561,997
Financial Liabilities:
Certificates of deposit, Carrying Value	1,882,933	1,208,177
Certificates of deposit, Fair Value	1,867,124	1,174,230
Long-term FHLB advances, Carrying Value	325,000	25,000
Long-term FHLB advances, Fair Value	326,507	23,001
Subordinated debt, Carrying Value	194,596	194,264
Subordinated debentures, Fair Value	144,443	160,933
U.S. government agencies
Financial Assets:
Carrying Value	10,598	11,099
Fair Value	9,917	10,385
Mortgage-backed securities, residential
Financial Assets:
Carrying Value	339,427	360,683
Fair Value	268,310	302,612
Collateralized mortgage obligations, residential
Financial Assets:
Carrying Value	12,474	13,026
Fair Value	9,412	10,456
Mortgage-backed securities, multifamily
Financial Assets:
Carrying Value	5,024	5,094
Fair Value	4,141	4,347
Obligations of states and political subdivisions
Financial Assets:
Carrying Value	477,297	530,506
Fair Value	362,673	430,108
Corporate bonds
Financial Assets:
Carrying Value	2,879	2,900
Fair Value	2,272	2,547
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Fair Value	0	0
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Long-term FHLB advances, Fair Value	0	0
Subordinated debentures, Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. government agencies
Financial Assets:
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-backed securities, residential
Financial Assets:
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Collateralized mortgage obligations, residential
Financial Assets:
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Mortgage-backed securities, multifamily
Financial Assets:
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Obligations of states and political subdivisions
Financial Assets:
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Corporate bonds
Financial Assets:
Fair Value	0	0
Significant Other Observable Inputs (Level 2)
Financial Assets:
Fair Value	651,746	758,982
Federal Home Loan Bank and other membership bank stocks, Fair Value	53,580	42,483
Fair Value	0	0
Financial Liabilities:
Certificates of deposit, Fair Value	1,867,124	1,174,230
Long-term FHLB advances, Fair Value	326,507	23,001
Subordinated debentures, Fair Value	0	0
Significant Other Observable Inputs (Level 2) \| U.S. government agencies
Financial Assets:
Fair Value	9,917	10,385
Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities, residential
Financial Assets:
Fair Value	268,310	302,612
Significant Other Observable Inputs (Level 2) \| Collateralized mortgage obligations, residential
Financial Assets:
Fair Value	9,412	10,456
Significant Other Observable Inputs (Level 2) \| Mortgage-backed securities, multifamily
Financial Assets:
Fair Value	4,141	4,347
Significant Other Observable Inputs (Level 2) \| Obligations of states and political subdivisions
Financial Assets:
Fair Value	357,694	428,635
Significant Other Observable Inputs (Level 2) \| Corporate bonds
Financial Assets:
Fair Value	2,272	2,547
Significant Unobservable Inputs (Level 3)
Financial Assets:
Fair Value	4,979	1,473
Federal Home Loan Bank and other membership bank stocks, Fair Value	0	0
Fair Value	7,722,899	7,561,997
Financial Liabilities:
Certificates of deposit, Fair Value	0	0
Long-term FHLB advances, Fair Value	0	0
Subordinated debentures, Fair Value	144,443	160,933
Significant Unobservable Inputs (Level 3) \| U.S. government agencies
Financial Assets:
Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Mortgage-backed securities, residential
Financial Assets:
Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Collateralized mortgage obligations, residential
Financial Assets:
Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Mortgage-backed securities, multifamily
Financial Assets:
Fair Value	0	0
Significant Unobservable Inputs (Level 3) \| Obligations of states and political subdivisions
Financial Assets:
Fair Value	4,979	1,473
Significant Unobservable Inputs (Level 3) \| Corporate bonds
Financial Assets:
Fair Value	$ 0	$ 0

Certificate of deposits fair value disclosure.

No definition available.

Name:	lbai_CertificateOfDepositsFairValueDisclosure
Namespace Prefix:	lbai_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount excluding accrued interest, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ 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 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

+ Details

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

- Definition

Fair value of subordinated debt obligations including, but not limited to, subordinated loan, subordinated bond, subordinated debenture or junior debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

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

- Definition

Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480876/942-470-45-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480848/942-470-50-2

+ Details

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

- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 325
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481026/942-325-45-1

+ Details

Name:	us-gaap_FederalHomeLoanBankStock
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

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

+ References

+ Details

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

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

+ Details

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

- Definition

Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-10

+ Details

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

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- Definition

Amount of time deposit liabilities, including certificates of deposit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 405
-Topic 942
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481047/942-405-50-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateBondSecuritiesMember
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: