Significant Accounting Policies Self-Insurance Accruals (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Abstract]
Health insurance reserves	$ 6.7htld_HealthInsuranceReserves	$ 6.1htld_HealthInsuranceReserves

Self insurance health insurance reserves for estimated cost of health related claims, including estimated expenses incurred but not reported

No definition available.

Name:	htld_HealthInsuranceReserves
Namespace Prefix:	htld_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant