| Document And Entity Information | Apr. 23, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 23, 2024 |
| Entity Registrant Name | SAIA, INC. |
| Entity Central Index Key | 0001177702 |
| Entity Emerging Growth Company | false |
| Entity File Number | 0-49983 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 48-1229851 |
| Entity Address, Address Line One | 11465 Johns Creek Parkway |
| Entity Address, Address Line Two | Suite 400 |
| Entity Address, City or Town | Johns Creek |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30097 |
| City Area Code | 770 |
| Local Phone Number | 232-5067 |
| Entity Information, Former Legal or Registered Name | No Changes. |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $.001 per share |
| Trading Symbol | SAIA |
| Security Exchange Name | NASDAQ |
