Loans and Leases and Other Real Estate - Allowance for Loan and Lease Losses by Portfolio Segment and Related Recorded Investment in Loans and Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 31,245	$ 30,874
Charge-offs	(3,446)	(4,655)
Recoveries	1,566	803
Provision	6,090	4,223	$ 1,942
Ending balance: Individually evaluated for impairment	505	529
Ending balance	35,455	31,245	30,874
Ending balance: Collectively evaluated for impairment	34,950	30,716
LOANS AND LEASES
Total Loans and Leases	4,156,680	3,873,895
LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	22,591	25,285
Ending balance: Collectively evaluated for impairment	4,133,379	3,847,202
Total Loans and Leases	4,156,680	3,873,895
LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	710	1,408
Commercial, secured by real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21,223	20,223
Charge-offs	(762)	(410)
Recoveries	396	297
Provision	4,847	1,113
Ending balance: Individually evaluated for impairment	454	392	598
Ending balance	25,704	21,223	20,223
Ending balance: Collectively evaluated for impairment	25,250	20,831
LOANS AND LEASES
Total Loans and Leases	2,831,184	2,556,601
Commercial, secured by real estate \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	17,536	18,624
Ending balance: Collectively evaluated for impairment	2,812,941	2,536,858
Total Loans and Leases	2,831,184	2,556,601
Commercial, secured by real estate \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	707	1,119
Commercial, industrial and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,723	2,637
Charge-offs	(477)	(796)
Recoveries	172	202
Provision	895	(320)
Ending balance: Individually evaluated for impairment	9	12	77
Ending balance	2,313	1,723	2,637
Ending balance: Collectively evaluated for impairment	2,304	1,711
LOANS AND LEASES
Total Loans and Leases	340,400	350,228
Commercial, industrial and other \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	782	952
Ending balance: Collectively evaluated for impairment	339,618	349,001
Total Loans and Leases	340,400	350,228
Commercial, industrial and other \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	0	275
Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	548	460
Charge-offs	(305)	(366)
Recoveries	59	31
Provision	328	423
Ending balance: Individually evaluated for impairment	30	0	1
Ending balance	630	548	460
Ending balance: Collectively evaluated for impairment	600	548
LOANS AND LEASES
Total Loans and Leases	75,039	67,016
Leases \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	65	0
Ending balance: Collectively evaluated for impairment	74,974	67,016
Total Loans and Leases	75,039	67,016
Leases \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	0	0
Real estate - residential mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,964	2,588
Charge-offs	(441)	(1,103)
Recoveries	5	8
Provision	29	471
Ending balance: Individually evaluated for impairment	4	31	73
Ending balance	1,557	1,964	2,588
Ending balance: Collectively evaluated for impairment	1,553	1,933
LOANS AND LEASES
Total Loans and Leases	322,880	349,581
Real estate - residential mortgage \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	1,744	2,911
Ending balance: Collectively evaluated for impairment	321,136	346,670
Total Loans and Leases	322,880	349,581
Real estate - residential mortgage \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	0	0
Real estate - construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,352	1,591
Charge-offs	(609)	0
Recoveries	31	18
Provision	957	743
Ending balance: Individually evaluated for impairment	0	0	21
Ending balance	2,731	2,352	1,591
Ending balance: Collectively evaluated for impairment	2,731	2,352
LOANS AND LEASES
Total Loans and Leases	264,908	211,109
Real estate - construction \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	1,471	1,471
Ending balance: Collectively evaluated for impairment	263,437	209,638
Total Loans and Leases	264,908	211,109
Real estate - construction \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	0	0
Home equity and consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,435	3,375
Charge-offs	(852)	(1,980)
Recoveries	903	247
Provision	(966)	1,793
Ending balance: Individually evaluated for impairment	8	94	73
Ending balance	2,520	3,435	$ 3,375
Ending balance: Collectively evaluated for impairment	2,512	3,341
LOANS AND LEASES
Total Loans and Leases	322,269	339,360
Home equity and consumer \| LOANS AND LEASES
LOANS AND LEASES
Ending balance: Individually evaluated for impairment	993	1,327
Ending balance: Collectively evaluated for impairment	321,273	338,019
Total Loans and Leases	322,269	339,360
Home equity and consumer \| LOANS AND LEASES \| Loans Acquired with Deteriorated Credit Quality
LOANS AND LEASES
Ending balance: Loans acquired with deteriorated credit quality	$ 3	$ 14

Provision recovery for loan and lease losses.

No definition available.

Name:	lbai_ProvisionRecoveryForLoanAndLeaseLosses
Namespace Prefix:	lbai_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

+ References

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

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

+ References

+ 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

+ 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

+ Details

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

- 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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 4: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-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=82894903&loc=d3e15032-111544

+ 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://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

+ Details

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

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_NotesReceivableNet
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_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
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: