LOANS (Loans by credit quality indicator narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans secured by residential real estate property in process of foreclosure	$ 1.8
Loans delinquent 30 to 89 days, percentage	0.22%	0.33%
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Percent of loans	60.00%
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Percent of loans	40.00%
Nonpass
Financing Receivable, Credit Quality Indicator [Line Items]
Percent of nonaccrual loans	14.00%

Financing Receivable, Recorded Investment, 30 to 89 Days Past Due, Percentage

No definition available.

Name:	htlf_FinancingReceivableRecordedInvestment30to89DaysPastDuePercentage
Namespace Prefix:	htlf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Financing Receivables, Recorded Investments, Nonaccrual Status, Percentage

+ References

No definition available.

+ Details

Name:	htlf_FinancingReceivablesRecordedInvestmentsNonaccrualStatusPercentage
Namespace Prefix:	htlf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans And Leases Receivable, Gross, Percentage

+ References

No definition available.

+ Details

Name:	htlf_LoansAndLeasesReceivableGrossPercentage
Namespace Prefix:	htlf_
Data Type:	num:percentItemType
Balance Type:	na
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

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL49126937-111524

+ Details

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

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=htlf_NonpassMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: