$(document).ready(function () {
  var fileTypes = ['doc','xls','pdf','mp3'];
 
  $('a').click(function () {
    var anchor = $(this);
    var href = anchor.attr('href');
    var hrefArray = href.split('.');
    var extension = hrefArray.pop();
    if ($.inArray(extension,fileTypes) != -1) {      
      pageTracker._trackPageview('/documents/' + href);
    }
  });
  
});