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Acquisition of Gordon Trucking, Inc. Potential Earn Out Schedule (Details) (USD $) | Dec. 31, 2017 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | Nov. 11, 2013
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Acquisition of Gordon Trucking [Abstract] |  |  |  |  |
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High | $ 8,000,000 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh | $ 6,000,000 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh | $ 6,000,000 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh | $ 20,000,000 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh | $ 20,000,000 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh
Earn Out Agreement |  |  | 13,600,000 htld_Businesscombinationcontingentconsiderationfairvalue | 13,600,000 htld_Businesscombinationcontingentconsiderationfairvalue |
Business Combination, Contingent Consideration, Liability, Current |  |  | 2,300,000 us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent |  |
business combination contingent consideration fair value non-current |  |  | $ 11,300,000 htld_Businesscombinationcontingentconsiderationfairvaluenoncurrent | $ 13,600,000 htld_Businesscombinationcontingentconsiderationfairvaluenoncurrent |

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