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<?xml version="1.0" encoding="windows-1252"?> |
<ownershipDocument> |
| <schemaVersion> X0306 </schemaVersion> |
| <documentType> 4 </documentType> |
| <periodOfReport> 2020-06-04 </periodOfReport> |
| <notSubjectToSection16> false </notSubjectToSection16> |
| <issuer> |
| | <issuerCik> 0001177702 </issuerCik> |
| | <issuerName> SAIA INC </issuerName> |
| | <issuerTradingSymbol> SAIA </issuerTradingSymbol> |
| | </issuer> |
| <reportingOwner> |
| | <reportingOwnerId> |
| | | <rptOwnerCik> 0001799742 </rptOwnerCik> |
| | | <rptOwnerName> COL DOUGLAS L </rptOwnerName> |
| | | </reportingOwnerId> |
| | <reportingOwnerAddress> |
| | | <rptOwnerStreet1> 11465 JOHNS CREEK PARKWAY, SUITE 400 </rptOwnerStreet1> |
| | | <rptOwnerStreet2></rptOwnerStreet2> |
| | | <rptOwnerCity> JOHNS CREEK </rptOwnerCity> |
| | | <rptOwnerState> GA </rptOwnerState> |
| | | <rptOwnerZipCode> 30097 </rptOwnerZipCode> |
| | | <rptOwnerStateDescription></rptOwnerStateDescription> |
| | | </reportingOwnerAddress> |
| | <reportingOwnerRelationship> |
| | | <isDirector> false </isDirector> |
| | | <isOfficer> true </isOfficer> |
| | | <isTenPercentOwner> false </isTenPercentOwner> |
| | | <isOther> false </isOther> |
| | | <officerTitle> Executive VP, CFO & Secretary </officerTitle> |
| | | <otherText></otherText> |
| | | </reportingOwnerRelationship> |
| | </reportingOwner> |
| <nonDerivativeTable> |
| | <nonDerivativeTransaction> |
| | | <securityTitle> |
| <value> Common Stock </value> |
| </securityTitle> |
| | | <transactionDate> |
| <value> 2020-06-04 </value> |
| </transactionDate> |
| | | <deemedExecutionDate> |
| <value> 2020-06-04 </value> |
| </deemedExecutionDate> |
| | | <transactionCoding> |
| <transactionFormType> 4 </transactionFormType> |
| <transactionCode> S </transactionCode> |
| <equitySwapInvolved> false </equitySwapInvolved> |
| </transactionCoding> |
| | | <transactionTimeliness></transactionTimeliness> |
| | | <transactionAmounts> |
| <transactionShares> |
| <value> 1000.00 </value> |
| </transactionShares> |
| <transactionPricePerShare> |
| <value> 111.75 </value> |
| </transactionPricePerShare> |
| <transactionAcquiredDisposedCode> |
| <value> D </value> |
| </transactionAcquiredDisposedCode> |
| </transactionAmounts> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 5227.00 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </nonDerivativeTransaction> |
| | </nonDerivativeTable> |
| <derivativeTable> |
| | <derivativeHolding> |
| | | <securityTitle> |
| <value> Phantom Stock </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <footnoteId id="F1"/> |
| </conversionOrExercisePrice> |
| | | <exerciseDate> |
| <footnoteId id="F2"/> |
| </exerciseDate> |
| | | <expirationDate> |
| <footnoteId id="F3"/> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 2738.522 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 2738.522 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeHolding> |
| | <derivativeHolding> |
| | | <securityTitle> |
| <value> Stock Options (Right to Buy) </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <value> 100.20 </value> |
| </conversionOrExercisePrice> |
| | | <exerciseDate> |
| <footnoteId id="F4"/> |
| </exerciseDate> |
| | | <expirationDate> |
| <value> 2027-02-06 </value> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 2820.00 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 2820.00 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeHolding> |
| | <derivativeHolding> |
| | | <securityTitle> |
| <value> Stock Options (Right to Buy) </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <value> 73.35 </value> |
| </conversionOrExercisePrice> |
| | | <exerciseDate> |
| <value> 2021-02-06 </value> |
| </exerciseDate> |
| | | <expirationDate> |
| <value> 2025-02-06 </value> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 1270.00 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 1270.00 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeHolding> |
| | <derivativeHolding> |
| | | <securityTitle> |
| <value> Stock Options (Right to Buy) </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <value> 66.03 </value> |
| </conversionOrExercisePrice> |
| | | <exerciseDate> |
| <value> 2022-02-07 </value> |
| </exerciseDate> |
| | | <expirationDate> |
| <value> 2026-02-07 </value> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 1580.00 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 1580.00 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeHolding> |
| | </derivativeTable> |
| <footnotes> |
| | <footnote id="F1"> The conversion rate of this derivative security on June 4, 2020 is 1.1774 resulting in 3,224.328 shares of common stock (underlying security in column 7). </footnote> |
| | <footnote id="F2"> Immediate </footnote> |
| | <footnote id="F3"> The shares of phantom stock become payable in the Company's common stock upon reporting person's termination of service as an employee, in accordance with the terms of the Plan. </footnote> |
| | <footnote id="F4"> Stock Options granted as part of the long-term incentive program approved by the Compensation Committee. One-third of the award vests each year on the anniversary of the grant date. </footnote> |
| | </footnotes> |
| <remarks></remarks> |
| <ownerSignature> |
| | <signatureName> /s/ Stephanie R. Maschmeier </signatureName> |
| | <signatureDate> 2020-06-08 </signatureDate> |
| | </ownerSignature> |
| </ownershipDocument> |