-- None. No documentation exists for this element. --

No definition available.

Name:	thff_FinancingReceivableAbstract
Namespace Prefix:	thff_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded Investment in financing receivables.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_NotesReceivableNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_UnallocatedFinancingReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityAxis=us-gaap_ReceivablesAcquiredWithDeterioratedCreditQualityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Allowance for Loan Losses (Details 1) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Ending Balance Attributable to Loans
Individually evaluated for impairment	$ 766	$ 625
Collectively evaluated for impairment	19,476	19,284
Ending Balance	20,242	19,909	$ 19,395	$ 18,773
Loans
Individually evaluated for impairment	13,578	10,082
Collectively evaluated for impairment	1,897,929	1,901,080
Total	1,913,329	1,913,022
Commercial Portfolio Segment [Member]
Ending Balance Attributable to Loans
Individually evaluated for impairment	766	619
Collectively evaluated for impairment	9,386	9,662
Ending Balance	10,152	10,281	9,377	9,731
Loans
Individually evaluated for impairment	9,500	9,619
Collectively evaluated for impairment	1,131,154	1,134,701
Total	1,142,476	1,146,180
Residential Portfolio Segment [Member]
Ending Balance Attributable to Loans
Individually evaluated for impairment	0	6
Collectively evaluated for impairment	1,389	1,449
Ending Balance	1,389	1,455	1,496	1,553
Loans
Individually evaluated for impairment	4,078	463
Collectively evaluated for impairment	433,270	436,944
Total	437,348	437,407
Consumer Portfolio Segment [Member]
Ending Balance Attributable to Loans
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	6,781	6,709
Ending Balance	6,781	6,709	6,334	5,767
Loans
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	333,505	329,435
Total	333,505	329,435
Unallocated
Ending Balance Attributable to Loans
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,920	1,464
Ending Balance	1,920	1,464	$ 2,188	$ 1,722
Receivables Acquired with Deteriorated Credit Quality [Member]
Ending Balance Attributable to Loans
Financing Receivable, Allowance for Credit Losses	0	0
Loans
Financing Receivable, Net	1,822	1,860
Receivables Acquired with Deteriorated Credit Quality [Member] \| Commercial Portfolio Segment [Member]
Ending Balance Attributable to Loans
Financing Receivable, Allowance for Credit Losses	0	0
Loans
Financing Receivable, Net	1,822	1,860
Receivables Acquired with Deteriorated Credit Quality [Member] \| Residential Portfolio Segment [Member]
Ending Balance Attributable to Loans
Financing Receivable, Allowance for Credit Losses	0	0
Loans
Financing Receivable, Net	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] \| Consumer Portfolio Segment [Member]
Ending Balance Attributable to Loans
Financing Receivable, Allowance for Credit Losses	0	0
Loans
Financing Receivable, Net	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] \| Unallocated
Ending Balance Attributable to Loans
Financing Receivable, Allowance for Credit Losses	$ 0	$ 0