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Significant Accounting Policies Property, Equipment and Depreciation (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Property, Plant and Equipment    
Amortization Period of Tires 2 years  
Accumulated Depreciation, Depletion and Amortization, Property, Plant and Equipment, Period Increase (Decrease) $ 3,300,000htld_Changeinestimatefinancialimpactnetoftax  
change in estimate financial impact, per share, net of tax 0.02htld_Changeinestimatefinancialimpactpersharenetoftax  
Communications and Utilities Expense [Member]    
Property, Plant and Equipment    
Depreciation 1,100,000us-gaap_Depreciation
/ htld_FinancialStatementLocationAxis
= htld_CommunicationsAndUtilitiesExpenseMember
700,000us-gaap_Depreciation
/ htld_FinancialStatementLocationAxis
= htld_CommunicationsAndUtilitiesExpenseMember
Tractors [Member]    
Property, Plant and Equipment    
Property, Plant, and Equipment, Salvage Value 15,000us-gaap_PropertyPlantAndEquipmentSalvageValue
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= htld_TractorsMember
 
Trailers [Member]    
Property, Plant and Equipment    
Property, Plant, and Equipment, Salvage Value $ 4,000us-gaap_PropertyPlantAndEquipmentSalvageValue
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= htld_TrailersMember
 
Minimum [Member] | Land Improvements and Buildings [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 5 years  
Minimum [Member] | Leasehold Improvements [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 5 years  
Minimum [Member] | Furniture and Fixtures [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 3 years  
Minimum [Member] | Shop and Service Equipment [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 3 years  
Minimum [Member] | Revenue Equipment [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 5 years  
Maximum [Member] | Land Improvements and Buildings [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 30 years  
Maximum [Member] | Leasehold Improvements [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 25 years  
Maximum [Member] | Furniture and Fixtures [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 5 years  
Maximum [Member] | Shop and Service Equipment [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 10 years  
Maximum [Member] | Revenue Equipment [Member]    
Property, Plant and Equipment    
Property, Plant and Equipment, Useful Life 7 years