Name:	thff_BusinessAcquisitionLossSharingAgreementLossesInExcessOfThresholdToBeReimbursedPercentage
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Data Type:	num:percentItemType
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Represents the percentage of losses on assets acquired under business combination and covered under loss-sharing agreement, to be reimbursed by FDIC, if losses are up to the threshold amount.

No definition available.

Name:	thff_BusinessAcquisitionLossSharingAgreementLossesUpToThresholdToBeReimbursedPercentage
Namespace Prefix:	thff_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the threshold amount of losses on assets acquired in a business combination to calculate the amount of reimbursement under the loss-sharing agreement.

No definition available.

Name:	thff_BusinessAquisitionLossSharingAgreementLossesOnAssetsThreshold
Namespace Prefix:	thff_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Loans and Leases Receivable, Net of Loans with Deteriorated Credit Quality, Covered

No definition available.

Name:	thff_LoansandLeasesReceivableNetofLoanswithDeterioratedCreditQualityCovered
Namespace Prefix:	thff_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of decreases to the indemnification asset due to cash payments received relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC).

No definition available.

Name:	us-gaap_FDICIndemnificationAssetCashPaymentsReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266