The amount of accumulated depreciation for right-of-use asset under finance lease.

No definition available.

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

- Definition

The remaining lease term for leases of the lessee.

+ References

No definition available.

+ Details

Name:	hrth_LesseeLeaseRemainingLeaseTerm
Namespace Prefix:	hrth_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The renewal term for leases of the lessee.

+ References

No definition available.

+ Details

Name:	hrth_LesseeLeaseRenewalTerm
Namespace Prefix:	hrth_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The termination period for leases of the lessee.

+ References

No definition available.

+ Details

Name:	hrth_LesseeLeaseTerminationPeriod
Namespace Prefix:	hrth_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of operating sublease.

+ References

No definition available.

+ Details

Name:	hrth_LesseeOperatingSubleaseLeaseTerm
Namespace Prefix:	hrth_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

+ Details

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

- Details

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

- Details

Name:	us-gaap_LeaseContractualTermAxis=hrth_SubleaseFullertonJacksonvilleAndManilaFacilitiesMember
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_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note D - Leases (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Note D - Leases (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Operating Lease, Right-of-Use Asset	$ 23,793		$ 17,679
Lessee, Lease, Termination Period (Year)	1 year
Finance Lease, Right-of-Use Asset, after Accumulated Amortization, Total	$ 957		1,138
Finance Lease, Right-of-Use Asset, Accumulated Depreciation	$ 500		$ 400
Minimum [Member]
Lessee, Lease Remaining Lease Term (Year)	1 year
Minimum [Member] \| Sublease Fullerton, Jacksonville and Manila Facilities [Member]
Lessee, Operating Sublease, Lease Term (Month)	150 days
Maximum [Member]
Lessee, Lease Remaining Lease Term (Year)	6 years
Lessee, Lease, Renewal Term (Year)	5 years
Maximum [Member] \| Sublease Fullerton, Jacksonville and Manila Facilities [Member]
Lessee, Operating Sublease, Lease Term (Month)	2 years 330 days
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset		$ 22,800
Operating Lease, Liability, Total				$ 23,900