innerHeight not calculating properly

I am using the following code to resize a div layer to the inner dimensions of the browser, the width works fine but the height is calculating at 133px, no matter what the resolution.  Any suggestions?
<style type="text/css">
#surveydiv
{
      position:absolute;
      top:0;
      left:0;
      background-color: #CC0033;
      border: solid 2px black;
      z-index: 10;

}
</style>
<div id="surveydiv">
</div>
<script type="text/javascript">
      var ns=(document.layers);
      var ie=(document.all);
      var w3=(document.getElementById && !ie);
function sizesurvey()
{
      if(ie)            adDiv=eval('document.all.surveydiv.style');
      else if(ns)      adDiv=eval('document.layers["surveydiv"]');
      else if(w3)      adDiv=eval('document.getElementById("surveydiv").style');
      if (ie){documentWidth=document.body.offsetWidth-4;
      documentHeight=document.body.offsetHeight;}      
      else if (ns){documentWidth=window.innerWidth;
      documentHeight=window.innerHeight;}
      else if (w3){documentWidth=self.innerWidth;
      documentHeight=self.innerHeight;}
      
      adDiv.width = documentWidth;
      adDiv.height = documentHeight;
      alert(documentHeight);
}
</script>