Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 25, 2021
Document Information [Line Items]
Entity Central Index Key	0000799167
Entity Registrant Name	MARTEN TRANSPORT LTD
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	0-15010
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	39-1140809
Entity Address, Address Line One	129 Marten Street
Entity Address, City or Town	Mondovi
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	54755
City Area Code	715
Local Phone Number	926-4216
Title of 12(b) Security	COMMON STOCK, PAR VALUE
Trading Symbol	MRTN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		82,942,839