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Fair Value of Financial Instruments and Fair Value Measurements - Schedule of Fair Value Measurements On Nonrecurring, Valuation Techniques (Details) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
One-to-Four Family Residential Real Estate Loans [Member]
Impaired Loans Fair Value Disclosure	$ 240	$ 240
Fair Value Measurements, Valuation Techniques	Sales comparison	Sales comparison
Fair Value Measurements, Unobservable inputs	Adjustment to appraised value	Adjustment to appraised value
One-to-Four Family Residential Real Estate Loans [Member] | Minimum [Member]
Fair Value Measurements Range	0.00%	0.00%
One-to-Four Family Residential Real Estate Loans [Member] | Maximum [Member]
Fair Value Measurements Range	25.00%	25.00%
Commercial Real Estate Loans [Member]
Impaired Loans Fair Value Disclosure	$ 144	$ 100
Fair Value Measurements, Valuation Techniques	Sales comparison	Sales comparison
Fair Value Measurements, Unobservable inputs	Adjustment to appraised value	Adjustment to appraised value
Fair Value Measurements Range	15.00%	15.00%
Commercial Loans [Member]
Impaired Loans Fair Value Disclosure	$ 661	$ 678
Fair Value Measurements, Valuation Techniques	Sales comparison	Sales comparison
Fair Value Measurements, Unobservable inputs	Adjustment to comparable sales	Adjustment to comparable sales
Commercial Loans [Member] | Minimum [Member]
Fair Value Measurements Range	0.00%	0.00%
Commercial Loans [Member] | Maximum [Member]
Fair Value Measurements Range	69.00%	75.00%
Agriculture Loans [Member]
Impaired Loans Fair Value Disclosure	$ 140	$ 405
Fair Value Measurements, Valuation Techniques	Sales comparison	Sales comparison
Fair Value Measurements, Unobservable inputs	Adjustment to appraised value	Adjustment to appraised value
Agriculture Loans [Member] | Minimum [Member]
Fair Value Measurements Range	0.00%	0.00%
Agriculture Loans [Member] | Maximum [Member]
Fair Value Measurements Range	30.00%	30.00%

X

- Definition

Fair Value Measurements, Valuation Techniques.

+ References

No definition available.

+ Details

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Namespace Prefix:	LARK_
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Period Type:	duration

X

- Definition

The range of Level 3 fair value measurements for impaired loans measured at fair value on a non-recurring basis.

+ References

No definition available.

+ Details

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Namespace Prefix:	LARK_
Data Type:	num:percentItemType
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X

- Definition

Fair Value Measurements, Unobservable inputs.

+ References

No definition available.

+ Details

Name:	LARK_FairValueMeasurementsUnobservableInputs
Namespace Prefix:	LARK_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as impaired loans disclosure.

+ References

No definition available.

+ Details

Name:	LARK_ImpairedLoansFairValueDisclosure
Namespace Prefix:	LARK_
Data Type:	xbrli:monetaryItemType
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X

- Details

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X

- Details

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X

- Details

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- Details

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X

- Details

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- Details

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X

- Details

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