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