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Regulatory Capital Requirements - Schedule of Compliance with Regulatory Capital Requirements for Mortgage Companies (Details) (Parenthetical) | 9 Months Ended | 12 Months Ended
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Sep. 30, 2018 | Dec. 31, 2017
Company's Regulatory Capital Requirements [Member] |  |
Tier one capital conversation buffer | 1.875% | 1.25%

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- Definition The percentage of capital buffer to be maintained other than minimum capital requirements. + References No definition available. + Details
Name: | LARK_TierOneCapitalConversationBuffer
Namespace Prefix: | LARK_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | dei_LegalEntityAxis=LARK_CompanysRegulatoryCapitalRequirementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |