insert caseDet;
                attDocument.OwnerId = UserInfo.getUserId();
                attDocument.ParentId = caseDet.id; // the record the file is attached to
                attDocument.IsPrivate = false;
                insert attDocument;

                    <div class="form-group form-group-sm">
                    <apex:outputLabel value="Attach Document" for="frmAttDocument" styleClass="control-label"></apex:outputLabel>
                    <apex:inputFile id="frmAttDocument" value="{!AttDocument.Body}" filename="{!AttDocument.name}"  styleClass="btn btn-file btn-primary" />
                    <div class="help-block with-errors"></div>
                </div>