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Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Percentage Of Customer Revenue | 41.00%wern_RevenueFromMajorCustomersPercentage | 40.00%wern_RevenueFromMajorCustomersPercentage | 40.00%wern_RevenueFromMajorCustomersPercentage
Accounts receivable recorded investment past due days | 90 |  |
Self Insurance Retention Liability | $ 2.0 wern_SelfInsuranceRetentionLiability | $ 2.0 wern_SelfInsuranceRetentionLiability | $ 2.0 wern_SelfInsuranceRetentionLiability
Self Insurance Retention Workers Compensation | 1.0 wern_SelfInsuranceRetentionWorkersCompensation |  |
Letters of Credit Outstanding, Amount | 32.7 us-gaap_LettersOfCreditOutstandingAmount |  |
State Of Nebraska [Member] |  |  |
Workers Compensation Insurance Bonds | 32.6 wern_WorkersCompensationInsuranceBonds / wern_EmployeeBenefitsAxis = wern_StateOfNebraskaMember |  |
Workers Compensation Insurance Carrier [Member] |  |  |
Workers Compensation Insurance Bonds | $ 6.9 wern_WorkersCompensationInsuranceBonds / wern_EmployeeBenefitsAxis = wern_WorkersCompensationInsuranceCarrierMember |  |

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The disclosure indicates the age when individual accounts are reviewed. + References No definition available. + Details
Name: | wern_AccountsReceivableRecordedInvestmentPastDueDays
Namespace Prefix: | wern_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The disclosure indicates the percentage of revenue generated by the largest customers. + References No definition available. + Details
Name: | wern_RevenueFromMajorCustomersPercentage
Namespace Prefix: | wern_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The disclosure indicates the amount of liability retained by the company (self-insured retention and deductible) for each bodily injury or property damage occurrence. + References No definition available. + Details
Name: | wern_SelfInsuranceRetentionLiability
Namespace Prefix: | wern_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The disclosure indicates the amount of liability retained by the company (self-insured retention) for each workers' compensation occurrence. + References No definition available. + Details
Name: | wern_SelfInsuranceRetentionWorkersCompensation
Namespace Prefix: | wern_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The disclosure indicates the amount of the bonds carried for workers' compensation insurance. + References No definition available. + Details
Name: | wern_WorkersCompensationInsuranceBonds
Namespace Prefix: | wern_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | wern_EmployeeBenefitsAxis=wern_StateOfNebraskaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | wern_EmployeeBenefitsAxis=wern_WorkersCompensationInsuranceCarrierMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |