Investment Securities (Amortized Cost and Fair Value of Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Amortized Cost	$ 68,371	$ 69,472
Gross Unrealized Gains	2,745	1,863
Gross Unrealized Losses	(4)	(134)
Fair Value	71,112	71,201
U.S. Government Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	2,010	2,011
Gross Unrealized Gains	373	134
Fair Value	2,383	2,145
Municipal bonds [Member]
Schedule of Investments [Line Items]
Amortized Cost	34,860	34,985
Gross Unrealized Gains	810	835
Gross Unrealized Losses	(1)	(1)
Fair Value	35,669	35,819
Collateralized mortgage obligations - private label [Member]
Schedule of Investments [Line Items]
Amortized Cost	20	23
Gross Unrealized Losses	(1)
Fair Value	19	23
Collateralized mortgage obligations - government sponsored entities [Member]
Schedule of Investments [Line Items]
Amortized Cost	25,368	27,081
Gross Unrealized Gains	967	393
Gross Unrealized Losses	(2)	(133)
Fair Value	26,333	27,341
Government National Mortgage Association [Member]
Schedule of Investments [Line Items]
Amortized Cost	158	162
Gross Unrealized Gains	17	14
Fair Value	175	176
Federal National Mortgage Association [Member]
Schedule of Investments [Line Items]
Amortized Cost	2,863	1,944
Gross Unrealized Gains	136	69
Fair Value	2,999	2,013
Federal Home Loan Mortgage Corporation [Member]
Schedule of Investments [Line Items]
Amortized Cost	3,037	3,211
Gross Unrealized Gains	234	156
Fair Value	3,271	3,367
Asset-backed securities - Private label [Member]
Schedule of Investments [Line Items]
Gross Unrealized Gains	197	215
Fair Value	197	215
Asset-backed securities - Government sponsored entities [Member]
Schedule of Investments [Line Items]
Amortized Cost	33	33
Gross Unrealized Gains	2	2
Fair Value	35	35
Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	68,349	69,450
Gross Unrealized Gains	2,736	1,818
Gross Unrealized Losses	(4)	(134)
Fair Value	71,081	71,134
Equity Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	22	22
Gross Unrealized Gains	9	45
Fair Value	$ 31	$ 67

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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