Loans and Allowance for Loan Losses - Schedule of Past Due Financing Receivables (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Loans, Total past due loans accruing	$ 2,224	$ 1,671
Loans, Non-accrual loans	6,688	5,236
Loan, Total past due and non-accrual loans	8,912	6,907
Loan, Total loans not past due	$ 487,583	$ 488,340
Percent of gross loans, 30-59 days delinquent and accruing	0.30%	0.24%
Percent of gross loans, 60-89 days delinquent and accruing	0.15%	0.10%
Percent of gross loans, 90 days or more delinquent and accruing	0.00%	0.00%
Percentage of gross loans, Total past due loans accruing	0.45%	0.34%
Percent of gross loans, Non-accrual loans	1.35%	1.06%
Percentage of Total past due and non-accrual loans	1.79%	1.40%
Percentage of Total loans not past due	98.21%	98.60%
Agriculture Loans [Member]
Loans, Total past due loans accruing	$ 23	$ 188
Loans, Non-accrual loans	1,393	482
Loan, Total past due and non-accrual loans	1,416	670
Loan, Total loans not past due	93,489	95,962
Municipal Loans [Member]
Loans, Total past due loans accruing
Loans, Non-accrual loans
Loan, Total past due and non-accrual loans
Loan, Total loans not past due	2,922	2,953
Consumer Loans [Member]
Loans, Total past due loans accruing	63	129
Loans, Non-accrual loans	41	45
Loan, Total past due and non-accrual loans	104	174
Loan, Total loans not past due	24,056	25,254
Commercial Loans [Member]
Loans, Total past due loans accruing	261	418
Loans, Non-accrual loans	1,567	1,528
Loan, Total past due and non-accrual loans	1,828	1,946
Loan, Total loans not past due	77,275	72,343
30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	1,487	1,200
30-59 Days Delinquent and Accruing [Member] \| Agriculture Loans [Member]
Loans, Total past due loans accruing		100
30-59 Days Delinquent and Accruing [Member] \| Municipal Loans [Member]
Loans, Total past due loans accruing
30-59 Days Delinquent and Accruing [Member] \| Commercial Loans [Member]
Loans, Total past due loans accruing		398
60-89 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	737	471
60-89 Days Delinquent and Accruing [Member] \| Agriculture Loans [Member]
Loans, Total past due loans accruing		88
60-89 Days Delinquent and Accruing [Member] \| Municipal Loans [Member]
Loans, Total past due loans accruing
60-89 Days Delinquent and Accruing [Member] \| Consumer Loans [Member]
Loans, Total past due loans accruing	2	23
60-89 Days Delinquent and Accruing [Member] \| Commercial Loans [Member]
Loans, Total past due loans accruing		20
90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
One-to-Four Family Residential Real Estate Loans [Member]
Loans, Total past due loans accruing	758	337
Loans, Non-accrual loans	779	442
Loan, Total past due and non-accrual loans	1,537	779
Loan, Total loans not past due	134,334	136,116
One-to-Four Family Residential Real Estate Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	728	131
One-to-Four Family Residential Real Estate Loans [Member] \| 60-89 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	30	206
One-to-Four Family Residential Real Estate Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Construction and Land Loan [Member]
Loans, Total past due loans accruing	223	134
Loans, Non-accrual loans	946	948
Loan, Total past due and non-accrual loans	1,169	1,082
Loan, Total loans not past due	17,217	19,001
Construction and Land Loan [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	223
Construction and Land Loan [Member] \| 60-89 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing		134
Construction and Land Loan [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Commercial Real Estate Loans [Member]
Loans, Total past due loans accruing	896	465
Loans, Non-accrual loans	1,962	1,791
Loan, Total past due and non-accrual loans	2,858	2,256
Loan, Total loans not past due	138,290	136,711
Commercial Real Estate Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	264	465
Commercial Real Estate Loans [Member] \| 60-89 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	632
Commercial Real Estate Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Commercial Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	188
Commercial Loans [Member] \| 60-89 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	73
Commercial Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Agriculture Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	23
Agriculture Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Municipal Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Municipal Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing
Consumer Loans [Member] \| 30-59 Days Delinquent and Accruing [Member]
Loans, Total past due loans accruing	61	106
Consumer Loans [Member] \| 90 Days or More Delinquent and Accruing [Member]
Loans, Total past due loans accruing

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

Loans, Non-accrual loans.

+ References

No definition available.

+ Details

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

- 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 not past due status.

+ References

No definition available.

+ Details

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

- 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

- 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_FinancialInstrumentAxis=LARK_CommercialLoansMember
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_FinancingReceivablesPeriodPastDueAxis=LARK_SixtyToEightyNineDaysDelinquentAndAccruingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=LARK_NinetyDaysOrMoreDelinquentAndAccruingMember
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:

- Details

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

- Details

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

- Details

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

- Details

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