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Note 3 - Long-Term Debt (Details Textual) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Long-term Line of Credit $ 0us-gaap_LineOfCredit  
Letters of Credit Outstanding, Amount 9,200,000us-gaap_LettersOfCreditOutstandingAmount  
Line of Credit Facility, Remaining Borrowing Capacity 40,800,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity  
Minimum [Member]    
Line of Credit Facility, Maximum Borrowing Capacity 50,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Maximum [Member]    
Line of Credit Facility, Maximum Borrowing Capacity $ 75,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Credit Facility [Member]    
Long-term Debt, Weighted Average Interest Rate   0.84%us-gaap_LongtermDebtWeightedAverageInterestRate
/ us-gaap_DebtInstrumentAxis
= mrtn_CreditFacilityMember