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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-12-21</periodOfReport>

    <issuer>
        <issuerCik>0001143921</issuerCik>
        <issuerName>Crescent Financial Bancshares, Inc.</issuerName>
        <issuerTradingSymbol>CRFN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001467870</rptOwnerCik>
            <rptOwnerName>PIEDMONT COMMUNITY BANK HOLDINGS, INC.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3600 GLENWOOD AVENUE, SUITE 300</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RALEIGH</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27612</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-12-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>6114104</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.75</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24864104</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-12-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>64</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.75</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24864168</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On November 8, 2011, Piedmont Community Bank Holdings, Inc. (&quot;Piedmont&quot;) commenced a tender offer for up to 6,442,105 shares of common stock, par value $0.001, of the Issuer at a price of $4.75 net per share in cash, without interest and less applicable withholding taxes. The tender offer expired at 5:00 p.m., New York City time, on December 21, 2011.  According to Computershare Trust Company, N.A., the depositary for the tender offer, as of the expiration of the tender offer, 6,114,104 shares of the Issuer's common stock had been validly tendered and not withdrawn pursuant to the tender offer.  Piedmont accepted for purchase pursuant to the terms of the tender offer all of the shares that were validly tendered and not withdrawn in the tender offer.</footnote>
        <footnote id="F2">On December 22, 2011, Piedmont purchased 64 additional shares of the Issuer's common stock that were delivered to Piedmont in the tender offer pursuant to Notice of Guaranteed Delivery.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Scott Custer, President and Chief Executive Officer</signatureName>
        <signatureDate>2011-12-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
