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v3.23.2

Allowance for Credit Losses - Additional Information (Details) $ in Thousands | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 USD ($) loan | Dec. 31, 2022 loan
Allowance for loan losses |  |
Number of modifications resulted in the permanent reduction | 0 | 0
Number of loans modified as TDR | 0 |
Number of loans modified that had a payment default | 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 by troubled debt restructurings. + References No definition available. + Details
Name: | thff_FinancingReceivableModificationsNumberOfContracts1
Namespace Prefix: | thff_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of financing receivables that have been modified with payment default. + References No definition available. + Details
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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
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Namespace Prefix: | thff_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Number of modifications resulted in permanent reduction in investment in the loan. + References No definition available. + Details
Name: | thff_NumberOfModificationsResultedInPermanentReductionInInvestment
Namespace Prefix: | thff_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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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_
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Balance Type: | na
Period Type: | duration