FAIR VALUE (Quantitative Information about Level 3 fair value measurements) (Details) - Significant Unobservable Inputs (Level 3) $ in Thousands	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	$ 6,805	$ 12,548
Loans receivable	$ 40,863	$ 59,973
Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input (percent)	0	0
Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned, measurement input (percent)	0.10	0.10
Commercial and industrial \| Commercial and industrial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 15,242	$ 23,422
Commercial and industrial \| Commercial and industrial \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Commercial and industrial \| Commercial and industrial \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	15.00%	12.00%
Commercial and industrial \| Owner occupied commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 2,631	$ 30,400
Commercial and industrial \| Owner occupied commercial real estate \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Commercial and industrial \| Owner occupied commercial real estate \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	10.00%	20.00%
Commercial and industrial \| Non-owner occupied commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 5,661	$ 0
Commercial and industrial \| Non-owner occupied commercial real estate \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Commercial and industrial \| Non-owner occupied commercial real estate \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	10.00%	10.00%
Commercial and industrial \| Real Estate Construction
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 675	$ 642
Commercial and industrial \| Real Estate Construction \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Commercial and industrial \| Real Estate Construction \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	10.00%	10.00%
Agricultural and agricultural real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 15,927	$ 4,768
Agricultural and agricultural real estate \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Agricultural and agricultural real estate \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	15.00%	10.00%
Residential real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable	$ 727	$ 741
Residential real estate \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	0.00%	0.00%
Residential real estate \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans receivable, measurement input (percent)	10.00%	10.00%
Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	$ 9,864	$ 4,069
Premises, furniture and equipment held for sale \| Appraisal discount \| Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale, measurement input (percent)	0.00%	0.00%
Premises, furniture and equipment held for sale \| Appraisal discount \| Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale, measurement input (percent)	10.00%	10.00%

Assets Held For Sale, Measurement Input

No definition available.

Name:	htlf_AssetsHeldForSaleMeasurementInput
Namespace Prefix:	htlf_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans Receivable, Measurement Input

+ References

No definition available.

+ Details

Name:	htlf_LoansReceivableMeasurementInput
Namespace Prefix:	htlf_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of assets held-for-sale that are not part of a disposal group.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 15
-Paragraph 4
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482309/360-10-15-4

+ Details

Name:	us-gaap_AssetsHeldForSaleNotPartOfDisposalGroup
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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 103
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-103

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-10

+ Details

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

- Definition

Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

+ Details

Name:	us-gaap_OtherRealEstateOwnedMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputAppraisedValueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=htlf_AgriculturalAndAgriculturalRealEstatePortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_PropertyPlantAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: