<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-08-20</periodOfReport>
    <issuer>
        <issuerCik>0001042064</issuerCik>
        <issuerName>NORTHWEST BANCORP INC</issuerName>
        <issuerTradingSymbol>NWSB</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001186996</rptOwnerCik>
            <rptOwnerName>HUBER TIMOTHY A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>301 SECOND AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WARREN,</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>16365</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>Sr. V.P., Business Banking</officerTitle></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>50930959</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>6832</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By IRA</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>2140</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By Wife's IRA</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>447.349</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>As Custodian for Son 1</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>447.349</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>As Custodian for Son 2</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>11965.704</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By 401-K</value></natureOfOwnership></ownershipNature></nonDerivativeHolding><nonDerivativeHolding><securityTitle><value>Northwest Bancorp, Inc. Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>7414.35</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By ESOP</value></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeHolding><securityTitle><value>Stock Options (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>9.78</value></conversionOrExercisePrice><exerciseDate><value>2001-10-18</value></exerciseDate><expirationDate><value>2011-10-17</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Northwest Bancorp, Inc.</value></underlyingSecurityTitle><underlyingSecurityShares><value>4300</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>4300</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Stock Options (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>13.302</value></conversionOrExercisePrice><exerciseDate><value>2002-08-21</value></exerciseDate><expirationDate><value>2012-08-21</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Northwest Bancorp, Inc.</value></underlyingSecurityTitle><underlyingSecurityShares><value>5100</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5100</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeTransaction><securityTitle><value>Stock Options (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>16.59</value></conversionOrExercisePrice><transactionDate><value>2003-08-20</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>5100</value><footnoteId id="F1"/></transactionShares><transactionPricePerShare><value>16.59</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2003-08-20</value></exerciseDate><expirationDate><value>2013-08-20</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Northwest Bancorp, Inc.</value></underlyingSecurityTitle><underlyingSecurityShares><value>5100</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5100</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">A 20% increment of this option became exercisable on August 20, 2003. This option will continue to become exercisable each August thereafter in 20% increments through August 20, 2007. Although these options were granted by the Board on August 20, 2003 the insider was not issued an agreement with specific grant information until November 6, 2003.</footnote></footnotes><remarks/><ownerSignature><signatureName>Timothy A. Huber</signatureName><signatureDate>2003-11-07</signatureDate></ownerSignature></ownershipDocument>

