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Equity Compensation And Employee Benefit Plans (Schedule Of Equity Compensation Performance Shares Activity) (Details) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014
Equity Compensation Arrangement by Share-based Payment Award [Abstract] |
Number of Performance Shares Nonvested at beginning of period | 0 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedNumberBeginningBalance
Number of Performance Shares granted | 183 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardGranted
Number of Performance Shares vested | 0 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsVestedinPeriod
Number of Performance Shares forfeited | 0 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsForfeitedinPeriod
Number of Performance Shares Nonvested at end of period | 183 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedNumberEndingBalance
Weighted Average Grant Date Fair Value Nonvested at beginning of period | $ 0.00 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedWeightedAverageGrantDateFairValueBeginningBalance
Weighted Average Grant Date Fair Value Shares granted | $ 25.06 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsGrantsinPeriodWeightedAverageGrantDateFairValue
Weighted Average Grant Date Fair Value Shares vested | $ 0.00 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsVestedinPeriodWeightedAverageGrantDateFairValue
Weighted Average Grant Date Fair Value Shares forfeited | $ 0.00 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsForfeituresWeightedAverageGrantDateFairValue
Weighted Average Grant Date Fair Value Nonvested at end of period | $ 25.06 wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedWeightedAverageGrantDateFairValueEndingBalance

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- Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardAbstract
Namespace Prefix: | wern_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of performance shares granted to participants. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardGranted
Namespace Prefix: | wern_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of performance shares that were forfeited during the reporting period. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsForfeitedinPeriod
Namespace Prefix: | wern_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average fair value as of the grant date of performance shares that were not exercised or put into effect as a result of the occurrence of a terminating event. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsForfeituresWeightedAverageGrantDateFairValue
Namespace Prefix: | wern_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on performance shares. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsGrantsinPeriodWeightedAverageGrantDateFairValue
Namespace Prefix: | wern_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of non-vested equity based performance shares that validly exist and are outstanding as of the beginning of the period. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedNumberBeginningBalance
Namespace Prefix: | wern_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of non-vested equity based performance shares that validly exist and are outstanding as of the end of the period. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedNumberEndingBalance
Namespace Prefix: | wern_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Definition The weighted average fair value of nonvested awards on performance shares for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units, beginning of period. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedWeightedAverageGrantDateFairValueBeginningBalance
Namespace Prefix: | wern_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The weighted average fair value of nonvested awards on performance shares for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsNonvestedWeightedAverageGrantDateFairValueEndingBalance
Namespace Prefix: | wern_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of performance awards that vested during the reporting period. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsVestedinPeriod
Namespace Prefix: | wern_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition The weighted average fair value as of grant date pertaining to performance shares for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + References No definition available. + Details
Name: | wern_EquityCompensationArrangementbySharebasedPaymentAwardPerformanceAwardsVestedinPeriodWeightedAverageGrantDateFairValue
Namespace Prefix: | wern_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration