Description of Business and Summary of Accounting Policies - Summary of Risk Retention Amounts Per Occurrence (Parenthetical) (Detail) - USD ($)	12 Months Ended	36 Months Ended
Feb. 28, 2019	Dec. 31, 2021
Schedule Of Retention Amounts For Uninsured Claims Per Occurrence Basis [Abstract]
Bodily injury and property damage	$ 10,000,000	$ 2,000,000

Uninsured claims amount retained for injuries and property damages per occurrence.

No definition available.

Name:	saia_UninsuredClaimsAmountRetainedForInjuriesAndPropertyDamagesPerOccurrence
Namespace Prefix:	saia_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration