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v3.23.3

Allowance for Credit Losses - Additional Information (Details) $ in Thousands | 9 Months Ended
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Sep. 30, 2023 USD ($) loan
Allowance for loan losses |
Number of loans modified that had a payment default | loan | 0
Minimum outstanding balance of non-homogeneous loans to be individually evaluated as to credit risk | $ | $ 100

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- Definition Number of financing receivables that have been modified with payment default. + References No definition available. + Details
Name: | thff_FinancingReceivableModificationsNumberOfContractsWithPaymentDefault
Namespace Prefix: | thff_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the minimum outstanding balance of loans to be individually reviewed and classified as to credit risk. Homogeneous loans (at all levels of outstanding balances) are not reviewed individually, but rather as part of a group. + References No definition available. + Details
Name: | thff_LoansAndLeasesReceivableMinimumOutstandingBalanceToBeIndividuallyEvaluated
Namespace Prefix: | thff_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- 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 Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-13 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1405 -Paragraph c -Publisher SEC + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration