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Operating Leases Operating Leases (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Operating Leased Assets [Line Items] |  |  |
Operating Leases, Rent Expense Revenue Equipment | $ 300 | $ 5,000 | $ 8,000
Terminal Facilities [Member] |  |  |
Operating Leased Assets [Line Items] |  |  |
Operating Leases, Rent Expense | 2,500 | 4,800 | 3,900
Terminal Facilities [Member] | Related Party [Member] |  |  |
Operating Leased Assets [Line Items] |  |  |
Operating Leases, Rent Expense | $ 0 | $ 800 | $ 1,600

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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=htld_TerminalFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LeaseArrangementTypeAxis=htld_RelatedPartyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |