XML 109 R96.htm IDEA: XBRL DOCUMENT
v3.20.4

RETIREMENT PLANS: (Details 4) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 100.00% | 100.00%
Employee Stock Ownership Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 100.00% | 100.00%
Other Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 6.00% | 4.00%
Other Securities [Member] | Employee Stock Ownership Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 1.00% | 2.00%
Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 63.00% | 63.00%
Equity Securities | Minimum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 25.00% |
Equity Securities | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 75.00% |
Equity Securities | Employee Stock Ownership Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 99.00% | 98.00%
Equity Securities | Employee Stock Ownership Plan | Minimum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 95.00% |
Equity Securities | Employee Stock Ownership Plan | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 99.00% |
Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 31.00% | 33.00%
Debt securities | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 50.00% |
Debt securities | Employee Stock Ownership Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 0.00% | 0.00%
Other Security Investments [Member] | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 20.00% |
Other Security Investments [Member] | Employee Stock Ownership Plan | Maximum |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Percentage of plan assets (percent) | 5.00% |

X
- Definition The percentage of plan assets during the period. + References No definition available. + Details
Name: | thff_DefinedBenefitPlanPercentageOfPlanAssets
Namespace Prefix: | thff_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis=thff_EmployeeStockOwnershipPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=thff_OtherSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_ConvertibleDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_OtherAggregatedInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |