| Document And Entity Information | Jul. 16, 2020 |
| Document Information [Line Items] | |
| Entity, Registrant Name | MARTEN TRANSPORT, LTD. |
| Document, Type | 8-K |
| Document, Period End Date | Jul. 16, 2020 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 0-15010 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | COMMON STOCK |
| Trading Symbol | MRTN |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000799167 |
