Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$ 23,142us-gaap_NetIncomeLoss	$ 14,339us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	45,720us-gaap_Depreciation	43,123us-gaap_Depreciation
Deferred income taxes	(2,286)us-gaap_DeferredIncomeTaxExpenseBenefit	(6,294)us-gaap_DeferredIncomeTaxExpenseBenefit
Gain on disposal of property and equipment	(5,504)	(4,647)
Non-cash equity compensation	1,770us-gaap_ShareBasedCompensation	1,304us-gaap_ShareBasedCompensation
Insurance and claims accruals, net of current portion	5,400	(1,200)
Other	(190)	203
Changes in certain working capital items:
Accounts receivable, net	20,374	(12,647)
Other current assets	19,361	(2,650)
Accounts payable	9,220	8,405
Other current liabilities	3,979	19,273
Net cash provided by operating activities	120,986	59,209
Cash flows from investing activities:
Additions to property and equipment	(108,735)	(30,864)
Proceeds from sales of property and equipment	23,870	14,818
Decrease in notes receivable	3,777	2,766
Net cash used in investing activities	(81,088)	(13,280)
Cash flows from financing activities:
Dividends on common stock	(3,602)us-gaap_PaymentsOfDividendsCommonStock	(3,636)us-gaap_PaymentsOfDividendsCommonStock
Repurchases of common stock	0	(12,880)
Tax withholding related to net share settlements of restricted stock awards	(368)	0
Stock options exercised	703	3,133
Excess tax benefits from equity compensation	186	218
Net cash used in financing activities	(3,081)	(13,165)
Effect of exchange rate fluctuations on cash	(158)	26
Net increase in cash and cash equivalents	36,659	32,790
Cash and cash equivalents, beginning of period	22,604	23,678
Cash and cash equivalents, end of period	59,263	56,468
Supplemental disclosures of cash flow information:
Interest paid	482us-gaap_InterestPaid	105us-gaap_InterestPaid
Income taxes paid	1,467us-gaap_IncomeTaxesPaidNet	1,344us-gaap_IncomeTaxesPaidNet
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	5,917us-gaap_NotesIssued1	3,452us-gaap_NotesIssued1
Change in fair value of interest rate swap	87	0
Property and equipment acquired included in accounts payable	585	507
Property and equipment disposed included in other receivables	$ 68	$ 469

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- Definition

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromStockOptionsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_SupplementalCashFlowInformationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The net change during the reporting period in self insurance claims reserves expected to be paid after one year (or one business cycle).

+ References

No definition available.

+ Details

Name:	wern_IncreaseDecreaseInSelfInsuranceReservesNoncurrent
Namespace Prefix:	wern_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Property and equipment disposed included in other receivables

+ References

No definition available.

+ Details

Name:	wern_PropertyAndEquipmentDisposedIncludedInOtherReceivables
Namespace Prefix:	wern_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration