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Note 5 - Related Party Transactions (Details Textual) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Purchase of Fuel, Tires and Related Services [Member]
Related Party Transaction, Amounts of Transaction	$ 140,000	$ 124,000
Tire Purchases [Member]
Related Party Transaction, Amounts of Transaction	$ 1,000,000.0	$ 1,200,000

X

- Definition

Amount of transactions with related party during the financial reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

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

X

- Details

Name:	us-gaap_NatureOfExpenseAxis=mrtn_PurchaseOfFuelTiresAndRelatedServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_NatureOfExpenseAxis=mrtn_TirePurchasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: