GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Book value, fair value of commercial serving rights and impairment) (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Valuation Allowance	$ 1,700,000
15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,622,000	$ 1,522,000
Fair Value	1,187,000	1,100,000
Valuation Allowance	435,000	422,000
30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	6,340,000	5,445,000
Fair Value	4,614,000	4,089,000
Valuation Allowance	1,726,000	1,356,000
Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	51,000	87,000
Fair Value	211,000	203,000
Valuation Allowance	0	0
More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	499,000	776,000
Fair Value	747,000	1,085,000
Valuation Allowance	$ 0	$ 0

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.

No definition available.

+ Details

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

- Definition

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122739-111746

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

+ Details

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

- Definition

Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

+ Details

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

- Definition

Amount of increase (decrease) in the amortized amount from a decrease (increase) in the valuation allowance applied to the servicing asset for a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

+ Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=htlf_MortgageServicingRights15YearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=htlf_MortgageServicingRights30YearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=htlf_CommercialServicingRightslessthan20YearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=htlf_CommercialServicingRightsmorethan20YearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: