I would disable the postbackurl:
PostBackUrl ="JavaScript.Void(1);"
then change javascript function:
<script type="text/javascript">
function openwindow(id) {
window.open("AllPageDetails.aspx?id=" + id, "mywindow", "menubar=1,resizable=1,width=350,height=250");
}
</script>
And pass this id from your OnClientClick:
OnClientClick="openwindow(1);"
After that you will handle this is on the server side to display the proper result.