Document And Entity Information Note To Financial Statement Details Textual Note 2 - Adoption of New Accounting Standard Note 3 - Revenue and Business Segments Note 4 - Earnings Per Common Share Note 2 - Adoption of New Accounting Standard - Cumulative Effect of Adjustments for New Accounting Pronouncements on Consolidated Condensed Balance Sheet (Details) Note 2 - Adoption of New Accounting Standard - Impact of New Standard on Consolidated Condensed Balance Sheet and Statements of Operations (Details) Note 3 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) Note 4 - Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) Notes To Financial Statements Category of Item Purchased [Axis] Notes To Financial Statements [Abstract] Long-term Purchase Commitment, Category of Item Purchased [Domain] us-gaap_StockOptionPlanExpense Stock or Unit Option Plan Expense Other assets us-gaap_LiabilitiesCurrent Total current liabilities Other us-gaap_Revenues Operating revenue Operating expenses (income): Depreciation us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 Stockholders' Equity Note, Stock Split, Conversion Ratio us-gaap_DepreciationDepletionAndAmortization Depreciation, Depletion and Amortization, Total us-gaap_AssetsCurrent Total current assets us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest Total stockholders’ equity Balance Balance Common stock, $.01 par value per share; 96,000,000 shares authorized; 54,589,542 shares at March 31, 2018, and 54,533,455 shares at December 31, 2017, issued and outstanding Adjustments to reconcile net income to net cash provided by operating activities: Common stock, shares authorized (in shares) Accounts payable and accrued liabilities Common stock, shares issued (in shares) Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Range [Domain] Maximum [Member] Supplemental non-cash disclosure: Minimum [Member] Product and Service [Axis] Product and Service [Domain] Range [Axis] Investment, Name [Domain] Proceeds from revenue equipment dispositions Preferred stock, $.01 par value per share; 2,000,000 shares authorized; no shares issued and outstanding Preferred stock, shares issued (in shares) Interest us-gaap_PolicyTextBlockAbstract Accounting Policies Investment, Name [Axis] Preferred stock, shares authorized (in shares) Preferred stock, par value (in dollars per share) Insurance and claims accruals Operating revenue us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Revenue equipment additions Effect of dilutive stock options (in shares) Income taxes Liabilities: Current liabilities: Treasury Stock [Text Block] Supplemental disclosure of cash flow information: us-gaap_Assets Total assets mrtn_EquityMethodInvestmentOwnershipPercentageByNonrelatedParty Equity Method Investment, Ownership Percentage by Non-related Party The percentage of ownership by a non-related party of common stock or equity participation in the investee accounted for under the equity method of accounting. Property and equipment: Cash flows provided by operating activities: Schedule of Segment Reporting Information, by Segment [Table Text Block] Statement [Line Items] us-gaap_NumberOfOperatingSegments Number of Operating Segments Trade, net us-gaap_NumberOfReportableSegments Number of Reportable Segments Building [Member] Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Additional paid-in capital Stockholders’ equity: Adjustments for Change in Accounting Principle [Axis] Property, Plant and Equipment, Type [Axis] Adjustments for Change in Accounting Principle [Domain] us-gaap_NonoperatingIncomeExpense Other Segment Reporting Disclosure [Text Block] Property, Plant and Equipment, Type [Domain] Prepaid expenses and other Current assets: Fair Value Disclosures [Text Block] Net income Net income Net income Assets: us-gaap_NetCashProvidedByUsedInFinancingActivities Net cash used for financing activities us-gaap_Liabilities Total liabilities us-gaap_OperatingIncomeLoss Operating income Operating Income Employee Stock Option [Member] us-gaap_NetCashProvidedByUsedInOperatingActivities Net cash provided by operating activities us-gaap_NetCashProvidedByUsedInInvestingActivities Net cash used for investing activities Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] us-gaap_CashAndCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect Net change in cash and cash equivalents Accounting Standards Update 2014-09 [Member] Receivables: Purchased transportation Costs of purchased transportation and other third-party services incurred to service customers Business Combination Disclosure [Text Block] Commitments and Contingencies Disclosure [Text Block] us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Accumulated depreciation Operating taxes and licenses us-gaap_PropertyPlantAndEquipmentNet Net property and equipment Revenue Equipment [Member] Represents information pertaining to the "revenue equipment" category of property, plant and equipment. Stock Split Disclosure [Text Block] The entire disclosure for the reporting entity's stock splits. Buildings And Land Office Equipment And Other [Member] Represents information pertaining to buildings and land, office equipment and other. M W L [Member] M w l member. Supplies and maintenance Revenue equipment, buildings and land, office equipment and other Type of Adoption [Domain] us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation Employee taxes paid in exchange for shares withheld Calculated under Revenue Guidance in Effect before Topic 606 [Member] Change in property and equipment not yet paid The increase (decrease) to the amount of future cash outflows to pay for purchases of fixed assets that have occurred. Fuel and fuel taxes Capital Addition Purchase Commitments [Member] us-gaap_LettersOfCreditOutstandingAmount Letters of Credit Outstanding, Amount Adjustments for New Accounting Pronouncements [Axis] Communications and utilities Credit Facility [Member] Credit facility member. Insurance and claims mrtn_LineOfCreditFacilityDividendRestrictionsPercentageOfNetIncomeLimit Line Of Credit Facility Dividend Restrictions Percentage Of Net Income Limit Line of credit facility dividend restrictions percentage of net income limit. Purchase of Fuel, Tires and Related Services [Member] Represents information about the purchase of fuel and tire services. Tire Purchases [Member] Represents information pertaining to tire purchases. us-gaap_PaymentsOfDividendsCommonStock Payments of Ordinary Dividends, Common Stock Dividends on common stock us-gaap_EquityMethodInvestmentOwnershipPercentage Equity Method Investment, Ownership Percentage Numerator: Denominator: Stock Split To [Member] The ratio of shares representing a stock transaction after the stock split conversion. Dividends [Text Block] Disclosure of information related to dividends paid during the period. Stock Split from [Member] The ratio of shares representing a stock transaction before the stock split conversion. Paid Quarterly [Member] Paid quarterly member. Operating income: Cash flows used for investing activities: us-gaap_RevenueFromRelatedParties Revenue from Related Parties Retained Earnings [Member] Earnings Per Share [Text Block] mrtn_AdjustmentsToAdditionalPaidInCapitalEmployeeTaxesPaidInExhangeForSharesWitheld Employee taxes paid in exchange for shares withheld The adjustment to APIC satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award. Unvested Performance Unit Awards [Member] Unvested performance unit awards member. Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Issuance of common stock from share-based payment arrangement exercises us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities Accounts payable and accrued liabilities us-gaap_RelatedPartyTransactionAmountsOfTransaction Related Party Transaction, Amounts of Transaction mrtn_CustomerContractTerm Customer Contract Term Duration of customer contracts. Additional Paid-in Capital [Member] Common Stock [Member] Related Party Transactions Disclosure [Text Block] us-gaap_StockRepurchaseProgramAuthorizedAmount1 Stock Repurchase Program, Authorized Amount us-gaap_IncreaseDecreaseInOtherAccruedLiabilities Insurance and claims accruals us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased Stock Repurchase Program, Number of Shares Authorized to be Repurchased Income taxes expense Equity Components [Axis] Equity Component [Domain] Truckload [Member] Truckload member. Dedicated [Member] Dedicated segment provides customized transportation solutions tailored to meet individual customers’ requirements, utilizing temperature-controlled trailers, dry vans and other specialized equipment within the United States. Intermodal [Member] One of the company's segments that transports freight within the US, primarily utilizing our temperature controlled containers or to lesser extent contracted carriers. Brokerage [Member] One of the company's segments that arranges for small third party carriers to transport freight for our customers. Also includes MWL revenues. Revenue, Net of Fuel Surcharge [Member] Represents revenue from segment net of fuel surcharge revenue. Fuel Surcharge Revenue [Member] Represents revenue from fuel surcharges. us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest Income before income taxes Total operating expenses us-gaap_LineOfCredit Long-term Line of Credit, Total Cash and cash equivalents Beginning of period End of period Salaries, wages and benefits Share-based payment arrangement compensation expense us-gaap_AllocatedShareBasedCompensationExpense Amendment Flag Accounting Policies [Abstract] Significant Accounting Policies [Text Block] us-gaap_RepaymentsOfLongTermLinesOfCredit Repayment of borrowings under credit facility and long-term debt us-gaap_CommonStockDividendsPerShareDeclared Common Stock, Dividends, Per Share, Declared Dividends declared per common share (in dollars per share) us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption Cumulative Effect of New Accounting Principle in Period of Adoption Adoption of accounting standard (Note 2) us-gaap_LongtermDebtWeightedAverageInterestRate Long-term Debt, Weighted Average Interest Rate, at Point in Time us-gaap_SharesOutstanding Balance (in shares) Balance (in shares) Common stock, shares outstanding (in shares) Preferred stock, shares outstanding (in shares) Current Fiscal Year End Date Receivable Type [Axis] Receivable [Domain] Trade Accounts Receivable [Member] us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets Prepaid expenses and other Document Fiscal Period Focus Borrowings under credit facility and long-term debt Document Fiscal Year Focus Document Period End Date Nonmonetary Transaction Type [Domain] Document Type Interim Period, Costs Not Allocable [Domain] us-gaap_DividendsCommonStockCash Dividends on common stock Nonmonetary Transaction Type [Axis] Document Information [Line Items] Document Information [Table] Nature of Expense [Axis] Entity Filer Category Debt Instrument [Axis] Cumulative Effect of Adjustments for New Accounting Pronouncements on Balance Sheet [Table Text Block] Tabular disclosure of cumulative effect of adjustments for new accounting pronouncements on balance sheet. Entity Current Reporting Status Debt Instrument, Name [Domain] Entity Voluntary Filers Entity Well-known Seasoned Issuer Segments [Axis] Segments [Domain] mrtn_AdoptionOfAccountingStandard Adoption of accounting standard (Note 2) Represents the amount of adjustments to reconcile net income to net cash provide in operating activities related to adoption of accounting standard. us-gaap_IncreaseDecreaseInReceivables Receivables us-gaap_DueToAffiliateCurrentAndNoncurrent Due to Affiliate us-gaap_AdjustmentsToAdditionalPaidInCapitalStockSplit Cash in lieu of fractional shares from stock split Recent Accounting Pronouncements [Text Block] The entire disclosure of recent accounting pronouncements. us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding Diluted earnings per common share - weighted-average shares and assumed conversions (in shares) Share-based payment arrangement compensation expense us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear Purchase Obligation, Future Minimum Payments, Remainder of Fiscal Year Entity Central Index Key Entity Registrant Name Entity [Domain] Legal Entity [Axis] Statement [Table] Scenario [Axis] Statement of Financial Position [Abstract] Diluted earnings per common share (in dollars per share) Scenario, Unspecified [Domain] us-gaap_WeightedAverageNumberOfSharesOutstandingBasic Basic earnings per common share - weighted-average shares (in shares) Basic earnings per common share (in dollars per share) Statement of Cash Flows [Abstract] Entity Common Stock, Shares Outstanding (in shares) Statement of Stockholders' Equity [Abstract] us-gaap_StockRepurchasedAndRetiredDuringPeriodShares Stock Repurchased and Retired During Period, Shares Income Statement [Abstract] Trading Symbol Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity Line of Credit Facility, Remaining Borrowing Capacity us-gaap_GainLossOnDispositionOfAssets Gain on disposition of assets us-gaap_TableTextBlock Notes Tables us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] us-gaap_DueFromAffiliates Due from Affiliates us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares) Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards us-gaap_PaymentsForProceedsFromOtherInvestingActivities Other Cash flows used for financing activities: us-gaap_LiabilitiesAndStockholdersEquity Total liabilities and stockholders’ equity Deferred income taxes us-gaap_OtherCostAndExpenseOperating Other mrtn_StockIssuedDuringPeriodPercentageOfSharesStockSplit Stock Issued During Period, Percentage of Shares, Stock Split Increase in the number of shares during the period, as a percentage, as a result of a stock split. Dividends [Axis] Dividends [Domain] Retained earnings Debt Disclosure [Text Block] Changes in other current operating items: us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Class of Stock [Axis] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Cash and cash equivalents: us-gaap_EquityMethodInvestmentDividendsOrDistributions Distribution from affiliate us-gaap_IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions Equity in (earnings) loss from affiliate us-gaap_DeferredIncomeTaxExpenseBenefit Deferred income taxes