window.onload = function(){

        //高さ合わせるIDを指定
        var id = new Array("content_and_sidebar", "sidebar");
        var idHeight = new Array();
        var maxHeight = 0;

        //指定IDの高さを取得
        for(i=0; i<id.length; i++){
            idHeight[i] = document.getElementById(id[i]).offsetHeight;
        }

        //最大の高さをmaxHeightに格納
        for(i=0; i<id.length-1; i++){
            maxHeight = Math.max(maxHeight,idHeight[i]);
        }

        //一番高いのに合わせる
        for(i=0; i<id.length; i++){
            document.getElementById(id[i]).style.height = maxHeight + "px";
        }
    }