LOANS (Troubled debt narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($) loan	Mar. 31, 2021 USD ($)	Dec. 31, 2021 loan
Financing Receivable, Credit Quality Indicator [Line Items]
Post- Modification Recorded Investment	$ 0	$ 0
Recorded Investment	$ 0	$ 0
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loan relationships \| loan	0		0

Financing Receivable, Number of Loans

No definition available.

Name:	htlf_FinancingReceivableNumberofLoans
Namespace Prefix:	htlf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Details

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