Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 14, 2022	Jun. 30, 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	FY
Document Fiscal Year Focus	2021
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 1,064,500,000
Entity Common Stock, Shares Outstanding		83,040,704
Auditor Name	GRANT THORNTON LLP
Auditor Location	Minneapolis, Minnesota
Auditor Firm ID	248
ICFR Auditor Attestation Flag	true