Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Jul. 25, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Entity Registrant Name	Saia, Inc.
Entity Central Index Key	0001177702
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		26,411,736
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	0-49983
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	48-1229851
Document Quarterly Report	true
Document Transition Report	false
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
Title of each class	Common Stock, par value $.001 per share
Trading Symbol	SAIA
Security Exchange Name	NASDAQ