$(document).ready(function() {

  var heightL = $("#sidebarLeft").height();
  var heightR = $("#sidebarRight").height();
  var height  = $("#content").height();

  if(heightL > heightR) {
    if(heightL > height) $("#content").css("height",heightL);
  }
  else {
    if(heightR > height) $("#content").css("height",heightR);
  }

});