Significant Accounting Policies Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Significant Accounting Policies [Abstract]
PortionOfTaxBenefitRecordedPositionsMoreLikelyThanNotToBeSustained	50.00%
Valuation Allowance Against Any Deferred Tax Asset	$ 0	$ 0

PortionOfTaxBenefitRecordedPositionsMoreLikelyThanNotToBeSustained

No definition available.

Name:	htld_Portionoftaxbenefitrecordedpositionsmorelikelythannottobesustained
Namespace Prefix:	htld_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration