Fair Value (Details 2) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2016	Dec. 31, 2015
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	0.00%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	50.00%
State and Municipal Obligations \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 4,210	$ 4,725
Valuation Technique(s)	Discounted cash flow	Discounted cash flow
Unobservable Inputs	Discount rate Probability of default	Discount rate Probability of default
State and Municipal Obligations \| Minimum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	3.05%	3.05%
State and Municipal Obligations \| Maximum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	5.50%	5.50%
Other Real Estate \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 2,837	$ 3,466
Valuation Technique(s)	Sales comparison/income approach	Sales comparison/income approach
Unobservable Inputs	Discount rate for age of appraisal and market conditions	Discount rate for age of appraisal and market conditions
Other Real Estate \| Minimum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	5.00%	5.00%
Other Real Estate \| Maximum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	20.00%	20.00%
Impaired Loans \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 1,813	$ 2,352
Valuation Technique(s)	Sales comparison/income approach	Sales comparison/income approach
Unobservable Inputs	Discount rate for age of appraisal and market conditions	Discount rate for age of appraisal and market conditions
Impaired Loans \| Minimum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	0.00%	0.00%
Impaired Loans \| Maximum [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Range of Inputs	50.00%	50.00%

The description of the unobservable input used to measure the fair value of assets at the end of the period.

No definition available.

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

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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

- 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

No definition available.

+ Details

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Description of the inputs and valuation technique(s) used to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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