Allow Only Numbers in TextBox

<asp:TextBox ID="txtFareAmount_Travel_TEB" runat="server" MaxLength="12" CssClass="inptxt"
                                                            onBlur="CalculateGrandTotal_TEB(this.id)" onKeyup="ValidateDeciPointRevCalc(this.id)" ></asp:TextBox>
                                                            <asp:FilteredTextBoxExtender ID="ftbEx_txtFareAmount_Travel_TEB" runat="server" TargetControlID="txtFareAmount_Travel_TEB"
                                                                            FilterType="Custom, Numbers" ValidChars="."></asp:FilteredTextBoxExtender>