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Significant Accounting Policies Trade Receivables and Allowance for Doubtful Accounts (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 D | Dec. 31, 2013
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Significant Accounting Policies [Abstract] |  |
Customer credit terms (in days) | 30 htld_CustomerCreditTermsDays |
Allowance for Doubtful Accounts Receivable, Current | $ 1.3 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent | $ 1.0 us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent

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- Definition customer credit terms days + References No definition available. + Details
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Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: | htld_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 4 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.4) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant