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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-06-05</periodOfReport>

    <issuer>
        <issuerCik>0001568669</issuerCik>
        <issuerName>PENNYMAC FINANCIAL SERVICES, INC.</issuerName>
        <issuerTradingSymbol>PFSI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001469142</rptOwnerCik>
            <rptOwnerName>Botein Matthew</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O PENNYMAC FINANCIAL SERVICES, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>3043 TOWNSGATE ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESTLAKE VILLAGE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>91361</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-06-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>728</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25893</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Cl A Units of Private Nat'l Mortgage Acceptance Company, LLC</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2013-11-05</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>818552</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>818552</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These shares of Class A Common Stock were sold pursuant to a 10b5-1 plan.</footnote>
        <footnote id="F2">The reported amount consists of 10,128 restricted stock units and 15,765 shares of Class A Common Stock.  The restricted stock units are to be settled in an equal number of shares of Class A Common Stock upon vesting.</footnote>
        <footnote id="F3">Pursuant to the terms of an exchange agreement, Class A Units of Private National Mortgage Acceptance Company, LLC are exchangeable for shares of Class A Common Stock of PennyMac Financial Services, Inc. on a one-for-one basis, subject to customary conversion rate adjustments.</footnote>
        <footnote id="F4">N/A</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Kisha Parker, attorney-in-fact for Mr. Botein</signatureName>
        <signatureDate>2018-06-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
