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Concentrations of Credit Risk and Major Customers (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 Customer | Dec. 31, 2013 | Dec. 31, 2012
Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Concentration of risk, number of customers |  |  |  |  |  |  |  |  | 5 htld_ConcentrationOfRiskNumberOfCustomers |  |
Entity-Wide Revenue, Major Customer, Amount | $ 202,997 us-gaap_Revenues | $ 217,092 us-gaap_Revenues | $ 226,785 us-gaap_Revenues | $ 224,481 us-gaap_Revenues | $ 183,348 us-gaap_Revenues | $ 130,645 us-gaap_Revenues | $ 133,992 us-gaap_Revenues | $ 134,273 us-gaap_Revenues | $ 871,355 us-gaap_Revenues | $ 582,257 us-gaap_Revenues | $ 545,745 us-gaap_Revenues
Sales Revenue, Services, Net [Member] | Customer Concentration Risk [Member] |  |  |  |  |  |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Concentration of risk, number of customers |  |  |  |  |  |  |  |  | 0 htld_ConcentrationOfRiskNumberOfCustomers / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 0 htld_ConcentrationOfRiskNumberOfCustomers / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 1 htld_ConcentrationOfRiskNumberOfCustomers / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember
Baseline percentage for customer concentration of risk |  |  |  |  |  |  |  |  | 10.00%htld_Baselinepercentageforcustomerconcentrationofrisk / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 10.00%htld_Baselinepercentageforcustomerconcentrationofrisk / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 10.00%htld_Baselinepercentageforcustomerconcentrationofrisk / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember
Concentration Risk, Percentage |  |  |  |  |  |  |  |  | 32.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 32.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 39.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember
Accounts Receivable [Member] | Customer Concentration Risk [Member] |  |  |  |  |  |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |  |  |  |  |  |
Concentration Risk, Percentage |  |  |  |  |  |  |  |  | 28.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 20.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |

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- Definition Baseline percentage for customer concentration of risk + References No definition available. + Details
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- Definition Concentration of risk, number of customers + References No definition available. + Details
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- Details
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 + Details
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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 + Details
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