var name = "#sidebar";
var menuYloc = null;
  
$(document).ready(function(){  
    menuYloc = parseInt($(name).css("top").substring(0,$(name).css("top").indexOf("px")));
    $(window).scroll(function () {  
        var offset = menuYloc+$(document).scrollTop()+"px";
        $(name).animate({top:offset},{duration:500,queue:false});
    });
});