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

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- 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

- 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

- 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

- 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

- Details

Name:	wern_EmployeeBenefitsAxis=wern_StateOfNebraskaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	wern_EmployeeBenefitsAxis=wern_WorkersCompensationInsuranceCarrierMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: