Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 98,650us-gaap_NetIncomeLoss	$ 86,785us-gaap_NetIncomeLoss	$ 103,034us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	176,984us-gaap_Depreciation	173,019us-gaap_Depreciation	166,957us-gaap_Depreciation
Deferred income taxes	5,038us-gaap_DeferredIncomeTaxExpenseBenefit	(8,389)us-gaap_DeferredIncomeTaxExpenseBenefit	(9,068)us-gaap_DeferredIncomeTaxExpenseBenefit
Gain on disposal of property and equipment	(19,260)	(16,408)	(20,533)
Non-cash equity compensation	6,070us-gaap_ShareBasedCompensation	4,809us-gaap_ShareBasedCompensation	4,602us-gaap_ShareBasedCompensation
Insurance and claims accruals, net of current portion	(8,455)	6,400	4,250
Other	1,107	(541)	(237)
Changes in certain working capital items:
Accounts receivable, net	(35,080)	(20,514)	7,579
Other current assets	(25,926)	3,398	17,581
Accounts payable	(1,497)	2,793	(20,172)
Other current liabilities	8,934	1,105	1,103
Net cash provided by operating activities	206,565	232,457	255,096
Cash flows from investing activities:
Additions to property and equipment	(296,649)	(211,329)	(284,942)
Retirements of property and equipment	84,355	59,413	60,015
Decrease in notes receivable	14,390	10,679	8,122
Other	(5,583)	979	0
Net cash used in investing activities	(203,487)	(140,258)	(216,805)
Cash flows from financing activities:
Repayments of short-term debt	(10,000)us-gaap_RepaymentsOfLinesOfCredit	(20,000)us-gaap_RepaymentsOfLinesOfCredit	(160,000)us-gaap_RepaymentsOfLinesOfCredit
Proceeds from issuance of short-term debt	10,000us-gaap_ProceedsFromLinesOfCredit	0us-gaap_ProceedsFromLinesOfCredit	180,000us-gaap_ProceedsFromLinesOfCredit
Repayments of long-term debt	(40,000)	(40,000)	0
Proceeds from issuance of long-term debt	75,000	10,000	70,000
Change in net checks issued in excess of cash balances	0	0	(6,671)
Dividends on common stock	(14,440)us-gaap_PaymentsOfDividendsCommonStock	(14,587)us-gaap_PaymentsOfDividendsCommonStock	(124,391)us-gaap_PaymentsOfDividendsCommonStock
Repurchases of common stock	(30,587)	(20,060)	0
Tax withholding related to net share settlements of restricted stock awards	(1,977)	(1,804)	(674)
Stock options exercised	7,012	2,548	6,035
Excess tax benefits from equity compensation	1,324	379	150
Net cash used in financing activities	(3,668)	(83,524)	(35,551)
Effect of exchange rate fluctuations on cash	(484)	(425)	276
Net increase (decrease) in cash and cash equivalents	(1,074)	8,250	3,016
Cash and cash equivalents, beginning of period	23,678	15,428	12,412
Cash and cash equivalents, end of period	22,604	23,678	15,428
Supplemental disclosures of cash flow information:
Interest paid	820us-gaap_InterestPaid	466us-gaap_InterestPaid	245us-gaap_InterestPaid
Income taxes paid	76,849us-gaap_IncomeTaxesPaidNet	66,032us-gaap_IncomeTaxesPaidNet	67,968us-gaap_IncomeTaxesPaidNet
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	14,385us-gaap_NotesIssued1	17,110us-gaap_NotesIssued1	10,564us-gaap_NotesIssued1
Issuance of notes payable	6,233us-gaap_NotesAssumed1	0us-gaap_NotesAssumed1	0us-gaap_NotesAssumed1
Change in fair value of interest rate swap	(1,180)	0	0
Property and equipment acquired included in accounts payable	2,067	5,403	109
Property and equipment disposed included in other receivables	$ 0	$ 434	$ 311

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Period Type:	duration

- Definition

Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

+ References

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Period Type:	duration

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with principal collections from a borrowing supported by a written promise to pay an obligation.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph f

-Article 4

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

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

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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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Data Type:	xbrli:monetaryItemType
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- Definition

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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Data Type:	xbrli:monetaryItemType
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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

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-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

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

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- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph f

-Article 4

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

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

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- Definition

The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

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

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- 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.

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
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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

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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.

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Namespace Prefix:	wern_
Data Type:	xbrli:monetaryItemType
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