function get_doc_height (doc) {
  var docHt = 0;
  var sh;
  var oh;

  if (doc.height) {
    docHt = doc.height;
  } else if (doc.body) {
    if (doc.body.scrollHeight) docHt = sh = doc.body.scrollHeight;
    if (doc.body.offsetHeight) docHt = oh = doc.body.offsetHeight;
    if (sh && oh) docHt = Math.max(sh, oh);
  }

  return docHt;
}