Allowance for Loan Losses Allowance for Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Modifications [Line Items]
Beginning Balance	$ 14,758	$ 21,285
Added	628	201
Charged Off	102	1,089
Payments	256	2,088
Ending Balance	15,028	14,325
Commercial
Financing Receivable, Modifications [Line Items]
Beginning Balance	8,955	12,327
Added	0	0
Charged Off	0	1,069
Payments	120	1,915
Ending Balance	8,835	9,343
Residential
Financing Receivable, Modifications [Line Items]
Beginning Balance	5,189	4,330
Added	579	133
Charged Off	62	0
Payments	88	101
Ending Balance	5,618	4,362
Consumer
Financing Receivable, Modifications [Line Items]
Beginning Balance	614	644
Added	49	68
Charged Off	40	20
Payments	48	72
Ending Balance	$ 575	$ 620

Financing Receivable, Impaired, Troubled Debt Restructuring, Additions During Period

No definition available.

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Namespace Prefix:	thff_
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Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable, Impaired, Troubled Debt Restructuring, Payments During Period

+ References

No definition available.

+ Details

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Namespace Prefix:	thff_
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- Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

+ Details

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- Details

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- Details

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- Details

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