v3.26.1

Leases - Supplemental Balance Sheet Information (Details) - USD ($)	Dec. 31, 2025	Dec. 31, 2024
Leases [Abstract]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Right-of-use Assets	Right-of-use Assets
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Right-of-use Assets	Right-of-use Assets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Short-term lease liabilities	Short-term lease liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Short-term lease liabilities	Short-term lease liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term lease liabilities	Long-term lease liabilities
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term lease liabilities	Long-term lease liabilities
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Short-term lease liabilities, Long-term lease liabilities	Short-term lease liabilities, Long-term lease liabilities
Operating Leases, Right-of-use Assets	$ 19,247,000	$ 21,678,000
Finance Leases, Right-of-use Assets	607,000	782,000
Right-of-use Assets	19,854,000	22,460,000
Operating Leases, Short-term lease liabilities	3,376,000	3,578,000
Finance Leases, Short-term lease liabilities	167,000	158,000
Short-term lease liabilities	3,543,000	3,736,000
Operating Leases, Long-term lease liabilities	18,400,000	20,235,000
Finance Leases, Long-term lease liabilities	461,000	625,000
Long-term lease liabilities	18,861,000	20,860,000
Operating Leases, Total Lease Liabilities	21,776,000	23,813,000
Finance Leases, Total Lease Liabilities	628,000	783,000
Total Lease Liabilities	$ 22,404,000	$ 24,596,000

Present value of lessee's discounted obligation for lease payments from operating and finance leases.

+ References

No definition available.

+ Details

Name:	hrth_OperatingAndFinanceLeaseLiability
Namespace Prefix:	hrth_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating and finance leases, classified as current.

+ References

No definition available.

+ Details

Name:	hrth_OperatingAndFinanceLeaseLiabilityCurrent
Namespace Prefix:	hrth_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating and finance leases, classified as noncurrent.

+ References

No definition available.

+ Details

Name:	hrth_OperatingAndFinanceLeaseLiabilityNoncurrent
Namespace Prefix:	hrth_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's right to use underlying asset under operating and finance leases.

+ References

No definition available.

+ Details

Name:	hrth_OperatingAndFinanceLeaseRightOfUseAsset
Namespace Prefix:	hrth_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

Name:	us-gaap_FinanceLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

Name:	us-gaap_FinanceLeaseLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Indicates line item in statement of financial position that includes current finance lease liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-2

+ Details

Name:	us-gaap_FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease, classified as noncurrent.

+ References

+ Details

Name:	us-gaap_FinanceLeaseLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Indicates line item in statement of financial position that includes noncurrent finance lease liability.

+ References

+ Details

Name:	us-gaap_FinanceLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Definition

Indicates line item in statement of financial position that includes finance lease liability.

+ References

+ Details

Name:	us-gaap_FinanceLeaseLiabilityStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after accumulated amortization, of right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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

- Definition

Indicates line item in statement of financial position that includes finance lease right-of-use asset.

+ References

+ Details

Name:	us-gaap_FinanceLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Indicates line item in statement of financial position that includes current operating lease liability.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Indicates line item in statement of financial position that includes noncurrent operating lease liability.

+ References

+ Details

Name:	us-gaap_OperatingLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

+ Details

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

- Definition

Indicates line item in statement of financial position that includes operating lease right-of-use asset.

+ References

+ Details

Name:	us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList
Namespace Prefix:	us-gaap_
Data Type:	enum2:enumerationSetItemType
Balance Type:	na
Period Type:	instant

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