Document And Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Feb. 27, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	MARTEN TRANSPORT LTD
Entity Central Index Key	0000799167
Trading Symbol	mrtn
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		54,565,778
Entity Public Float			$ 696,064
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Amendment Flag	false