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Profit Sharing Plan and Retirement Plan (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Profit Sharing Plan and Retirement Plan [Abstract] |  |  |
Defined Contribution Plan, Cost Recognized | $ 2.1 us-gaap_DefinedContributionPlanCostRecognized | $ 0.4 us-gaap_DefinedContributionPlanCostRecognized | $ 0.7 us-gaap_DefinedContributionPlanCostRecognized

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- Details
Name: | htld_ProfitSharingPlanAndRetirementPlanAbstract
Namespace Prefix: | htld_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration