<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-10-01</periodOfReport>

    <issuer>
        <issuerCik>0001145197</issuerCik>
        <issuerName>INSULET CORP</issuerName>
        <issuerTradingSymbol>PODD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001181286</rptOwnerCik>
            <rptOwnerName>LIAMOS CHARLES T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INSULET CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>600 TECHNOLOGY PARK DRIVE, SUITE 200</rptOwnerStreet2>
            <rptOwnerCity>BILLERICA</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01821</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-10-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.82</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>104733</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-10-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>36.58</value>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>100733</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>15.82</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2014-10-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-01-10</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>42000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 16,000 restricted stock units granted on April 1, 2012, which vest one-half of the total units on April 1, 2015 and one-half of the total units on April 1, 2016; 22,500 restricted stock units granted on March 1, 2013, which vest one-third of the total units on March 1, 2015, one-third of the total units on March 1, 2016 and one-third of the total units on March 1, 2017; 22,000 performance share units granted on March 1, 2013, which vest one-half of the total units on March 1, 2015 and one-half of the total units on March 1, 2016; and 4,000 restricted stock units granted on June 2, 2014, which vest one-half of the total units on April 30, 2015, one-quarter of the total units on April 30, 2016 and one-quarter of the total units on April 30, 2017.  Vested shares will be delivered to the reporting person as soon as practicable following a vesting date.</footnote>
        <footnote id="F2">Includes an aggregate of 1,166 shares acquired under the Insulet Corporation Amended and Restated 2007 Employee Stock Purchase Plan on the following dates:  357 shares acquired on June 29, 2012; 360 shares acquired on December 31, 2012; 243 shares acquired on June 28, 2013; and 206 shares acquired on December 31, 2013.</footnote>
        <footnote id="F3">The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 12, 2014.</footnote>
        <footnote id="F4">The price reported represents the weighted average sale price of the shares sold.  The shares were sold at varying prices in the range of $36.32 to $36.89.  The Reporting Person hereby undertakes, upon request of the Staff of the U.S. Securities Exchange Commission, the Issuer or a security holder of the Issuer, to provide full informaiton regarding the number of shares sold at each separate price.</footnote>
        <footnote id="F5">This option is subject to a four-year vesting period, with 25% of the total award vesting one year after the grant date and the remainder vesting in equal quarterly installments each quarter thereafter for 12 quarters, subject to continued employment.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ R. Anthony Diehl, attorney in fact</signatureName>
        <signatureDate>2014-10-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
