Loans and Other Real Estate - Allowance for Loan and Lease Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Loans	$ 5,331,863	$ 5,140,940
Ending Balance: Individually evaluated for impairment, related allowance	222	352
Ending Balance	48,884	40,003	$ 37,979	$ 37,688
Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	31,934	22,124
Ending Balance: Collectively evaluated for impairment	5,291,895	5,110,068
Ending Balance: Loans acquired with deteriorated credit quality	8,034	8,748
Total Loans	5,331,863	5,140,940
Ending Balance: Individually evaluated for impairment, related allowance	222	352
Ending Balance: Collectively evaluated for impairment, related allowance	48,662	39,651
Ending Balance	48,884	40,003
Commercial, secured by real estate
Financing Receivable, Past Due [Line Items]
Total Loans	3,740,319	3,589,593
Ending Balance: Individually evaluated for impairment, related allowance	202	228
Ending Balance	34,793	28,950	27,515	27,881
Commercial, secured by real estate \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	26,968	15,948
Ending Balance: Collectively evaluated for impairment	3,707,925	3,567,540
Ending Balance: Loans acquired with deteriorated credit quality	5,426	6,105
Total Loans	3,740,319	3,589,593
Ending Balance: Individually evaluated for impairment, related allowance	202	228
Ending Balance: Collectively evaluated for impairment, related allowance	34,591	28,722
Ending Balance	34,793	28,950
Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Total Loans	467,346	431,934
Ending Balance: Individually evaluated for impairment, related allowance	5	5
Ending Balance	5,489	3,289	2,592	1,742
Commercial, industrial and other \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	1,436	1,504
Ending Balance: Collectively evaluated for impairment	465,016	429,486
Ending Balance: Loans acquired with deteriorated credit quality	894	944
Total Loans	467,346	431,934
Ending Balance: Individually evaluated for impairment, related allowance	5	5
Ending Balance: Collectively evaluated for impairment, related allowance	5,484	3,284
Ending Balance	5,489	3,289
Equipment finance
Financing Receivable, Past Due [Line Items]
Total Loans	116,421	111,076
Ending Balance: Individually evaluated for impairment, related allowance	8	10
Ending Balance	1,257	957	947	987
Equipment finance \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	19	23
Ending Balance: Collectively evaluated for impairment	116,402	111,053
Ending Balance: Loans acquired with deteriorated credit quality	0	0
Total Loans	116,421	111,076
Ending Balance: Individually evaluated for impairment, related allowance	8	10
Ending Balance: Collectively evaluated for impairment, related allowance	1,249	947
Ending Balance	1,257	957
Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Total Loans	334,114	335,191
Ending Balance: Individually evaluated for impairment, related allowance	2	104
Ending Balance	1,600	1,725	1,564	1,566
Real estate - residential mortgage \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	2,179	2,315
Ending Balance: Collectively evaluated for impairment	331,534	332,486
Ending Balance: Loans acquired with deteriorated credit quality	401	390
Total Loans	334,114	335,191
Ending Balance: Individually evaluated for impairment, related allowance	2	104
Ending Balance: Collectively evaluated for impairment, related allowance	1,598	1,621
Ending Balance	1,600	1,725
Real estate - construction
Financing Receivable, Past Due [Line Items]
Total Loans	333,592	335,169
Ending Balance: Individually evaluated for impairment, related allowance	0	0
Ending Balance	3,344	2,672	2,887	3,015
Real estate - construction \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	694	1,663
Ending Balance: Collectively evaluated for impairment	332,101	332,722
Ending Balance: Loans acquired with deteriorated credit quality	797	784
Total Loans	333,592	335,169
Ending Balance: Individually evaluated for impairment, related allowance	0	0
Ending Balance: Collectively evaluated for impairment, related allowance	3,344	2,672
Ending Balance	3,344	2,672
Home equity and consumer
Financing Receivable, Past Due [Line Items]
Total Loans	340,071	337,977
Ending Balance: Individually evaluated for impairment, related allowance	5	5
Ending Balance	2,401	2,410	$ 2,474	$ 2,497
Home equity and consumer \| Loans and Leases
Financing Receivable, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment	638	671
Ending Balance: Collectively evaluated for impairment	338,917	336,781
Ending Balance: Loans acquired with deteriorated credit quality	516	525
Total Loans	340,071	337,977
Ending Balance: Individually evaluated for impairment, related allowance	5	5
Ending Balance: Collectively evaluated for impairment, related allowance	2,396	2,405
Ending Balance	$ 2,401	$ 2,410

Financial Asset Acquired with Credit Deterioration

No definition available.

Name:	lbai_FinancialAssetAcquiredwithCreditDeterioration
Namespace Prefix:	lbai_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=118939070&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=lbai_LoansAndLeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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