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Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Percentage Of Customer Revenue | 40.00% | 40.00% | 40.00%
Accounts receivable recorded investment past due days | 90 |  |
Liability Self-insurance Retention And Deductible Amount | $ 2.0 | $ 2.0 | $ 2.0
Self Insurance Retention Workers Compensation | 1.0 |  |
Letters of Credit Outstanding, Amount | 33.8 |  |
State Of Nebraska [Member] |  |  |
Workers Compensation Insurance Bonds | 32.2 |  |
Workers Compensation Insurance Carrier [Member] |  |  |
Workers Compensation Insurance Bonds | $ 6.9 |  |

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

X
- 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