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Significant Accounting Policies Revenue and Expense Recognition (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Significant Accounting Policies [Abstract] |  |  |
Fuel surcharge revenue | $ 170.4 htld_FuelSurchargeRevenue | $ 118.4 htld_FuelSurchargeRevenue | $ 112.4 htld_FuelSurchargeRevenue

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- Definition Fuel surcharge revenue + References No definition available. + Details
Name: | htld_FuelSurchargeRevenue
Namespace Prefix: | htld_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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