Loans and Allowance for Loan Losses - Schedule of Past Due Financing Receivables (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	1,475	1,355
Loans, Non-accrual loans	5,557	6,041
Loan, Total past due and non-accrual loans	7,032	7,396
Loan, Total loans not past due	$ 474,372	$ 431,840
Percent of gross loans, 30-59 days delinquent and accruing	0.18%	0.05%
Percent of gross loans, 60-89 days delinquent and accruing	0.13%	0.26%
Percent of gross loans, 90 days or more delinquent and accruing	0.00%	0.00%
Percentage of gross loans, Total past due loans accruing	0.31%	0.31%
Percent of gross loans, Non-accrual loans	1.15%	1.37%
Percentage of Total past due and non-accrual loans	1.46%	1.68%
Percentage of Total loans not past due	98.54%	98.32%
Commercial Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	119	397
Loans, Non-accrual loans	2,013	2,002
Loan, Total past due and non-accrual loans	2,132	2,399
Loan, Total loans not past due	65,766	52,192
Agriculture Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	344
Loans, Non-accrual loans	413	833
Loan, Total past due and non-accrual loans	757	833
Loan, Total loans not past due	90,619	82,175
Municipal Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing
Loans, Non-accrual loans
Loan, Total past due and non-accrual loans
Loan, Total loans not past due	2,990	3,396
Consumer Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	39	309
Loans, Non-accrual loans	80	34
Loan, Total past due and non-accrual loans	119	343
Loan, Total loans not past due	22,893	21,703
30-59 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	868	228
30-59 Days Delinquent and Accruing [Member] \| Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due	26
30-59 Days Delinquent and Accruing [Member] \| Agriculture Loan [Member]
Financing Receivable, Recorded Investment, Past Due	294
30-59 Days Delinquent and Accruing [Member] \| Municipal Loan [Member]
Financing Receivable, Recorded Investment, Past Due
30-59 Days Delinquent and Accruing [Member] \| Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due	35	105
60-89 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	607	1,127
60-89 Days Delinquent and Accruing [Member] \| Commercial Loan [Member]
Financing Receivable, Recorded Investment, Past Due	93	397
60-89 Days Delinquent and Accruing [Member] \| Agriculture Loan [Member]
Financing Receivable, Recorded Investment, Past Due	50
60-89 Days Delinquent and Accruing [Member] \| Municipal Loan [Member]
Financing Receivable, Recorded Investment, Past Due
60-89 Days Delinquent and Accruing [Member] \| Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due	4	204
One-To-Four Family Residential Real Estate Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	473	414
Loans, Non-accrual loans	588	552
Loan, Total past due and non-accrual loans	1,061	966
Loan, Total loans not past due	135,934	135,249
One-To-Four Family Residential Real Estate Loan [Member] \| 30-59 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	129	101
One-To-Four Family Residential Real Estate Loan [Member] \| 60-89 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	344	313
Construction and Land Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	273	4
Loans, Non-accrual loans	671	779
Loan, Total past due and non-accrual loans	944	783
Loan, Total loans not past due	29,897	18,573
Construction and Land Loan [Member] \| 30-59 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	157
Construction and Land Loan [Member] \| 60-89 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	116	4
Commercial Real Estate Loan [Member]
Loans, 90 days or more delinquent and accruing
Loans, Total past due loans accruing	227	231
Loans, Non-accrual loans	1,792	1,841
Loan, Total past due and non-accrual loans	2,019	2,072
Loan, Total loans not past due	126,273	118,552
Commercial Real Estate Loan [Member] \| 30-59 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due	227	22
Commercial Real Estate Loan [Member] \| 60-89 Days Delinquent and Accruing [Member]
Financing Receivable, Recorded Investment, Past Due		$ 209

Recorded investment in Financing receivables that are 30 days or more past due and accruing, total.

No definition available.

Name:	LARK_FinancingReceivableRecordedInvestment30DaysOrMorePastDueAndAccruingTotal
Namespace Prefix:	LARK_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage amount of Recorded investment in financing receivables that are 30 days or more past due and accruing, total.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestment30DaysOrMorePastDueAndAccruingTotalPercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage amount of financing receivables that are less than 60 days past due but more than 29 days past due.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestment30To59DaysPastDuePercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage amount of financing receivables that are less than 90 days past due but more than 59 days past due.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestment60To89DaysPastDuePercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage amount of Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruingPercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of financing receivables that are current.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestmentCurrentPercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage amount of Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestmentNonaccrualStatusPercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment that are past due including non accrual status.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestmentPastDueIncludingNonAccrualStatus
Namespace Prefix:	LARK_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of recorded investment that are past due including non accrual status.

+ References

No definition available.

+ Details

Name:	LARK_FinancingReceivableRecordedInvestmentPastDueIncludingNonAccrualStatusPercentage
Namespace Prefix:	LARK_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

+ Details

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

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

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

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=LARK_ThirtyToFiftyNineDaysDelinquentAndAccruingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=LARK_SixtyToEightyNineDaysDelinquentAndAccruingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=LARK_OneToFourFamilyResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=LARK_ConstructionAndLandLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: